How do I fix the Visual Studio compile error, "mismatch between processor architecture"?

Question

I'm new to project configuration in Visual Studio 2010, but I've done some research and still can't quite figure this issue out. I have a Visual Studio solution with a C++ DLL referencing the C# DLL. The C# DLL references a few other DLLs, some within my project and some external. When I try to compile the C++ DLL, I get this warning:

warning MSB3270: There was a mismatch between the processor architecture of the project being build "MSIL" and the processor architecture of the reference "[internal C# dll]", "x86".

It tells me to go to Configuration Manager to align my architectures. The C# DLL is set up with platform target x86. If I try to change this to something else, like Any CPU, it complains because one of the external DLLs it depends on has platform target x86.

When I look at Configuration Manager it shows the Platform for my C# DLL as x86 and for my C++ project as Win32. This seems like the right setup; surely I don't want the project for my C++ project to have platform set to x64, which is the only other option presented.

What am I doing wrong here?

• lordcheeto: What is the complaint, specifically, when you change it to Any CPU?
• lordcheeto: I don't have enough information to make an informed suggestion, but right-click on your solution -> Project Build Order and make sure that your C# project is getting built before the C++ project. If it's not, go to the Dependencies tab and let VS know that the C++ project depends on the C# project.
• Paul McCarthy: Visual Studio is again crap on this. Platform at the top of my screen says x64 but the warning says the project being built is "MSIL". So Visual studio is telling me that there is a mismatch between apples and oranges when I am not using apples. Can we rename it to Visual Stupido?
• Paul McCarthy: As far as I am concerned this is a bug in Visual Studio. I select x64 as platform target and it tells me that I the project is being build for MSIL.
• zar: The short answer is if your project has dependencies on x86 or x64, you can't use Any CPU (which is only for pure .NET applications). So you have to build for either x64 or x32, not Any CPU. This is derived from Dave's answer

Answer 1

This warning seems to have been introduced with the new Visual Studio 11 Beta and .NET 4.5, although I suppose it might have been possible before.

First, it really is just a warning. It should not hurt anything if you are just dealing with x86 dependencies. Microsoft is just trying to warn you when you state that your project is compatible with "Any CPU" but you have a dependency on a project or .dll assembly that is either x86 or x64. Because you have an x86 dependency, technically your project is therefore not "Any CPU" compatible. To make the warning go away, you should actually change your project from "Any CPU" to "x86". This is very easy to do, here are the steps.

1. Go to the Build|Configuration Manager menu item.
2. Find your project in the list, under Platform it will say "Any CPU"
3. Select the "Any CPU" option from the drop down and then select <New..>
4. From that dialog, select x86 from the "New Platform" drop down and make sure "Any CPU" is selected in the "Copy settings from" drop down.
5. Hit OK
6. You will want to select x86 for both the Debug and Release configurations.

This will make the warning go away and also state that your assembly or project is now no longer "Any CPU" compatible but now x86 specific. This is also applicable if you are building a 64 bit project that has an x64 dependency; you would just select x64 instead.

One other note, projects can be "Any CPU" compatible usually if they are pure .NET projects. This issue only comes up if you introduce a dependency (3rd party dll or your own C++ managed project) that targets a specific processor architecture.

• Tod Thomson: I just installed the RTW of Visual Studio 2012 and opened a preexisting 2010 solution and started seeing the same warning, so it's something that is still existing in the RTW.
• Tod Thomson: That being said, I think David's answer is correct, this warning is letting you know that your app really isn't "AnyCPU" so you will run into issues when you eventually deploy it to the wrong architecture.
• Yaur: It very well CAN hurt something. An Any CPU exe will load as x64 on a 64 bit OS and be unable to load x86 dlls. So if you have a dependency on a particular platform your really should set your platform correctly.
• Xonatron: The Build menu seems to be missing in VS C# 2010 Express. How do I get to it? I wish they wouldn't hide things.
• jrh: Note that if you work with the Windows Forms designer, which is in Visual Studio, which is x86 only, changing from "Any CPU" to "x64" can cause the designer to stop working.

Answer 2

This is a very stubborn warning and while it is a valid warning there are some cases where it cannot be resolved due to use of 3rd party components and other reasons. I have a similar issue except that the warning is because my projects platform is AnyCPU and I'm referencing an MS library built for AMD64. This is in Visual Studio 2010 by the way, and appears to be introduced by installing the VS2012 and .Net 4.5.

Since I can't change the MS library I'm referencing, and since I know that my target deployment environment will only ever be 64-bit, I can safely ignore this issue.

What about the warning? Microsoft posted in response to a Connect report that one option is to disable that warning. You should only do this is you're very aware of your solution architecture and you fully understand your deployment target and know that it's not really an issue outside the development environment.

You can edit your project file and add this property group and setting to disable the warning:

<PropertyGroup>
 <ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>None</ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>
</PropertyGroup>

• JohnC: The only other official MS reference to this solution that I've seen is in the Microsoft .NET Framework 4.5 RC Readme file. Strangely it was removed from the RTM Readme file.
• Jimmy: This works, but not for a variation of the warning: "Referenced assembly ... targets a different processor than the application". It would be great if there was a similar setting for this warning?
• Ben Voigt: "my projects platform is AnyCPU and I'm referencing an MS library built for AMD64"... This is WRONG. Since your target deployment is always 64-bit, you can set your platform to x64, which makes for a more appropriate error if your 64-bit assumption ever gets violated, and also prevents the warning.
• jrh: @BenVoigt a great idea in theory, but VS being a x86 process needs x86 builds of controls to run stuff like the Windows Forms Designer, even if your application will only ever be 64 bit. It's a valid, but unfortunate reason to use a false "Any CPU" build.
• Ben Voigt: @jrh: Then put the GUI in a DLL project, and build that as AnyCPU. The EXE needs to be marked with the right architecture to match the native dependencies. Proper separation of GUI from logic goes a long way (although it does still have its limits, such as when the native code is rendering part of the GUI, but then designer support is a lost cause unless you do builds of the entire project for both x86 and x64)

Answer 3

A good rule of thumb is "open DLLs, closed EXEs", that is:

• EXE targets the OS, by specifying x86 or x64.
• DLLs are left open (i.e., AnyCPU) so they can be instantiated within a 32-bit or a 64-bit process.

When you build an EXE as AnyCPU, all you're doing is deferring the decision on what process bitness to use to the OS, which will JIT the EXE to its liking. That is, an x64 OS will create a 64-bit process, an x86 OS will create an 32-bit process.

Building DLLs as AnyCPU makes them compatible to either process.

For more on the subtleties of assembly loading, see here. The executive summary reads something like:

• AnyCPU – loads as x64 or x86 assembly, depending on the invoking process
• x86 – loads as x86 assembly; will not load from an x64 process
• x64 – loads as x64 assembly; will not load from an x86 process

• Steve Robbins: This rule makes sense to me. But consider the following situation: Native.dll (x64) used by NetA.dll (Any CPU) used by NetB.dll (Any CPU) used by App1.exe (x64). There is no real problem here, but compiling NetA.dll gives me the warning. OK, since this assembly directly depends on Native.dll, I could mark it as x64 also. But then compiling NetB.dll complains. I want to keep NetB.dll as "Any CPU" because it is a common assembly used in a different, pure-dot-net application. I conclude that my only option is to suppress/ignore the warning. Yes?
• Gustavo Mori: Because of the dependency on Native.dll, your entire app/assembly lineage is now x64, whether your suppress the warning or not. While suppression works in your scenario, weird situations could arise in the future. For example, 1) assembly NetB is used in an x86 environment, where Nativex64 will not load, or 2) your customer wants an x86 version of App1.exe, and you compile happily, since NetB is marked as any CPU, but again, Nativex64 at the top of the stack will not load
• David Burg: While Gustavo's rule is a good principle, it cannot be used for the specific problem asked in this question as the project already has a dependency on a 3rd party assembly that didn't follow the rule (it's x86, not AnyCPU). Hence as long as the dependency is there the whole chain of projects must target x86 and nothing else.

Answer 4

The C# DLL is set up with platform target x86

Which is kind of the problem, a DLL doesn't actually get to choose what the bitness of the process will be. That's entirely determined by the EXE project, that's the first assembly that gets loaded so its Platform target setting is the one that counts and sets the bitness for the process.

The DLLs have no choice, they need to be compatible with the process bitness. If they are not then you'll get a big Kaboom with a BadImageFormatException when your code tries to use them.

So a good selection for the DLLs is AnyCPU so they work either way. That makes lots of sense for C# DLLs, they do work either way. But sure, not your C++/CLI mixed mode DLL, it contains unmanaged code that can only work well when the process runs in 32-bit mode. You can get the build system to generate warnings about that. Which is exactly what you got. Just warnings, it still builds properly.

Just punt the problem. Set the EXE project's Platform target to x86, it isn't going to work with any other setting. And just keep all the DLL projects at AnyCPU.

• Paul Eastlund: So, to be clear: I am not building the EXE, I am building a DLL to be run with someone else's EXE. Changing the platform target of the C# DLLs to Any CPU does not eliminate the warning. I'm wondering if this is a case of connect.microsoft.com/VisualStudio/feedback/details/728901/… -- I would ignore the warning itself but in fact the EXE is able to load the C# DLL but not the C++ DLL so I think this is a real problem.
• Hans Passant: Are you in fact using VS2010? It also wasn't clear at all that you couldn't load the C++/CLI DLL. What is the diagnostic? Update your questions with this essential info.
• Paul Eastlund: Hadn't posted about the load failure because I wasn't 100% sure it was connected, and on further debugging it turns out not to be. I am using VS2010. Updated question text. Very sorry for confusion
• Hans Passant: You didn't document any kind of error or exception related to loading the DLL. I cannot help you if you don't tell me what you know. Good luck with it.

Answer 5

I was getting the same warning i did this:

1. unload project
2. edit project properties i.e .csproj

3. add the following tag:

   <PropertyGroup>
    <ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>
    None
    </ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>
   </PropertyGroup>
   

4. Reload the project

• Tiny: This is not solving the issue. Its just disabling the warning for the particular project. But in some cases I find it a valid solution. Thanks!

Answer 6

I had this problem today and just looking the building configurations in Visual Studio wasn't helping because it showed Any CPU for both the project that wasn't building and the referenced project.

I then looked in the csproj of the referenced project and found this:

<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
<DebugType>pdbonly</DebugType>
<Optimize>true</Optimize>
<OutputPath>bin\Release\</OutputPath>
<DefineConstants>TRACE</DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
<PlatformTarget>x64</PlatformTarget>

Somehow this PlatformTarget got added in the middle of a config change and the IDE didn't seem to see it.

Removing this line from the referenced project solved my problem.

• SohamC: It took me an entire day to figure this out. Thanks a lot! :)

Answer 7

Use https://learn.microsoft.com/en-us/visualstudio/msbuild/customize-your-build#directorybuildprops-example:

• add a Directory.Build.props file to your solution folder
• paste this in it:

<Project>
 <PropertyGroup>
 <ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>None</ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>
 </PropertyGroup>
</Project>

Answer 8

If your C# DLL has x86-based dependencies, then your DLL itself is going to have to be x86. I don't really see a way around that. VS complains about changing it to (for example) x64 because a 64-bit executable can't load 32-bit libraries.

I'm a little confused about the configuration of the C++ project. The warning message that was provided for the build suggests that it was targeted for AnyCPU, because it reported the platform that it targeted was [MSIL], but you indicated that the configuration for the project was actually Win32. A native Win32 app shouldn't involve the MSIL - although it would likely need to have CLR support enabled if it is interacting with a C# library. So I think there are a few gaps on the information side.

Could I respectfully ask you review and post a bit more detail of the exact configuration of the projects and how they are inter-related? Be glad to help further if possible.

Answer 9

In addition to David Sacks answer, you may also need to go to the Build tab of the Project Properties and set Platform Target to x86 for the project that is giving you these warnings. Though you might expect it to be, this setting does not seem to be perfectly synchronized with the setting in the configuration manager.

Answer 10

I just change Platform target to "Any CPU" from Properties and it is done! Maybe you should have to create a Release build.

To do this:

Your Project Properties

Platform target

Answer 11

For C# projects, the target of x86 does what it sounds like. It says that this assembly only supports x86 architectures. Likewise for x64. Any CPU on the other hand says that I don't care which architecture, I support both. So, the next 2 questions are (1) what is the configuration of the executable that uses these dlls? and (2) what is the bitness of your OS/Computer? The reason I ask is because if your executable is compiled to run in 64-bit, then it NEEDS all dependencies to be able to run in 64-bit mode as well. Your Any CPU assembly should be able to be loaded, but perhaps it is referencing some other dependency that is only capable of running in x86 configuration. Check all dependencies and dependencies-of-dependencies to make sure everything is either "Any CPU" or "x64" if you plan to run the executable in 64-bit mode. Otherwise, you'll have issues.

In many ways, Visual Studio does not make compiling a mixture of Any CPU and various architecture dependent assemblies easy. It is doable, but it often requires that an assembly that would otherwise be "Any CPU" to have to be compiled separately for x86 and x64 because some dependency-of-a-dependency somewhere has two versions.

• Paul Eastlund: Is the configuration of the executable matter pertinent since I'm getting a failure just in trying to build the DLLs? (It's x86 though.) My computer is x64.
• Jonathan DeCarlo: It is the executable that determines what bitness will be used. If the executable is running as x64, then anything it loads (directly or indirectly) must be x64 or Any CPU. If the executable is running as x86, then anything is loads (directly or indirectly) must be x86 or Any CPU.

Answer 12

I am using IIS Express and the fix for me was to make sure my Web project had its bitness set to 64.

Bitness x64

Answer 13

I've had a similar problem before, specifically when adding a test solution to an existing x64 solution, like SharePoint. In my case, it seems to have to do with the fact that certain project templates are added as certain platforms by default.

Here's the solution that often works for me: set everything to the correct platform in the Configuration Manager (the active configuration drop-down, says Debug normally, is a good way to get to it) and project platform (in project properties), then build, then set everything back to AnyCPU. Sometimes I have to remove and re-add some dependencies (DLLs in each project's Properties) and sometimes the "Run tests in 32 bit or 64 bit process" (double-click Local.testsettings and go to Hosts) has to be changed.

It seems to me that this is just setting something then setting it back, but there's probably more going on behind the scenes that I'm not seeing. It's worked fairly consistently for me in the past though.

Answer 14

For my project, I have a requirement to be able to build to both x86 and x64. The problem with this is that whenever you add references while using one, then it complains when you build the other.

My solution is to manually edit the *.csproj files so that lines like these:

<Reference Include="MyLibrary.MyNamespace, Version=1.0.0.0, Culture=neutral, processorArchitecture=x86"/>
<Reference Include="MyLibrary.MyNamespace, Version=1.0.0.0, Culture=neutral, processorArchitecture=AMD64"/>
<Reference Include="MyLibrary.MyNamespace, Version=1.0.0.0, Culture=neutral, processorArchitecture=MSIL"/>

get changed to this:

<Reference Include="MyLibrary.MyNamespace, Version=1.0.0.0, Culture=neutral"/>

Answer 15

I had similar problem it was caused by MS UNIT Test DLL. My WPF application was compiled as x86 but unit test DLL (referenced EXE file) as "Any CPU". I changed unit test DLL to be compiled for x86 (same as EXE) and it was resovled.

Answer 16

You may also get this warning for MS Fakes assemblies which isn't as easy to resolve since the f.csproj is build on command. Luckily the Fakes xml allows you to add it in there.

Answer 17

I had a very similar warning in my build. My projects were set to target .NET 4.5, on the build server the Windows 8.1 SDK (for .NET 4.5.1) was installed. After updating my projects to target .NET 4.5.1 (wasn't a problem for me, was for a completely new application), I didn't receive the warning anymore...

Answer 18

I solved this warning changing "Configuration Manager" to Release (Mixed Plataform).

Answer 19

I got this warning in Visual Studio 2012 when compiling a SQL Server 2012 SP1 SSIS pipeline script task - until I installed SQL Server 2012 SP2.

Answer 20

I had the same problem with SQLite opening connection, and using the Nuget and installing the component used in project (SQLite) fixed it! try installing your component this way and check the result

Answer 21

Just want to post for those not finding the answers here solved their problem.

When running your application, make sure the solution platform drop down is correctly set. mine was on x86 which in turn caused me this problem.

Answer 22

I was having the same problem and tried a number of the answers provided without success. Eventually I found a solution - prompted by the answer posted by JBourne (on Mar 31, 2017 at 12:58). I inserted a PlatFormTarget property entry (set to anyCPU) into the PropertyGroup section in the .csproj file of the project, which was identified as the source of the process architecture mismatch error. The PropertyGroup entry then became:

<PropertyGroup>
<OutputType>WinExe</OutputType>
<TargetFramework>net6.0-windows10.0.22621.0</TargetFramework>
<PlatformTarget>anyCPU</PlatformTarget>
<Nullable>enable</Nullable>
<UseWPF>true</UseWPF>
<ApplicationIcon>Images\AppIcon.ico</ApplicationIcon>
<SupportedOSPlatformVersion>10.0.17763.0</SupportedOSPlatformVersion>

I rebuilt the parent package and, when I created its App Packages (Project/Publish/Create App Packages...), the error message had gone. The App Packages were created successfully.

Answer 23

Worth noting is that if you go and change the project output from x86 (or All CPUs) to x64, you sometimes can get this error until you close Visual Studio and then re-open the project.

Answer 24

For my situation it was where a programmer included as a reference the actual compiled file (the .DLL) instead of the project as a reference (the .csproj). Hence it was compiling against a final DLL which wasn't necessarily compatible with the primary exe/dll.

Answer 25

There should be a way to make a .NET EXE/DLL AnyCPU, and any unmanaged DLLs it depends on compiled both with x86 and x64, both bundled perhaps with different filenames and then the .NET module dynamically loading the correct one based on its runtime processor architecture. That would make AnyCPU powerful. If the C++ DLL only supports x86 or x64 then AnyCPU is of course pointless. But the bundling both idea I have yet to see implemented as the configuration manager does not even provide a means to build the same project twice with a different configuration/platform for multiple bundling allowing AnyCPU or even other concepts like any configuration to be possible.

• Corley Brigman: welcome to stackoverflow! can you try to focus/reformat this answer a little bit?
• Ben Voigt: This sounds like it would make a good question, or a blog post or a feature request on Connect... it doesn't actually answer this one.