Errors seen whilst compiling with AdaFruit Motor Shield ("invalid library")

Question

Whenever I compile a sketch, change the Tools> Board selection, or open/close Boards Manager/Library Manager I get the following message in the console:

> WARNING: Spurious .github folder in 'Adafruit Motor Shield library' library 
> WARNING: Spurious .github folder in 'Adafruit Motor Shield V2 Library' library
> 
> 
> Invalid library found in
> C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master:
> C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master
> Invalid library found in C:\arduino-1.6.8\libraries\robotarm:
> C:\arduino-1.6.8\libraries\robotarm Invalid library found in
> C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master:
> C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master
> Invalid library found in C:\arduino-1.6.8\libraries\robotarm:
> C:\arduino-1.6.8\libraries\robotarm

Answer 1

Arduino IDE 1.6.6 and higher are picky about what you have in your libraries folders. There are two general valid library formats, the old "pre-1.5" format and the newer 1.5 format, the specification of which is at https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5:-Library-specification.

Any folder in any of the Arduino libraries folder that doesn't follow a valid library format will cause the "Invalid library" message. Common causes of this issue are:

• Putting a sketch folder in the libraries folder. Libraries may contain example sketches but a sketch by itself is not allowed.
• Libraries that are in a subfolder, rather than the library folder being in the root of the libraries folder as required.

Now lets look at your specific messages:

Invalid library found in C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master: C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master

By looking at the Adafruit-Motor-Shield-for-Arduino repository we see that it's not a library but the PCB design files for the shield and thus has no business being in the libraries folder. Please move it to a different location.

Invalid library found in C:\arduino-1.6.8\libraries\robotarm: C:\arduino-1.6.8\libraries\robotarm

Without being able to see what's in this folder I can't say exactly the problem. If you will provide a directory listing I could update this answer with specific directions. As it is now, that folder is doing you no good in the libraries folder.