Hi Scuri
Very sorry to have wasted your time, but thank you for looking into it for me. It was a path issue. I copied all the DLLs into the same folder as the release executable, but then tested it by running a debug executable which was located in a different folder. Iup.dll and lua53.dll loaded fine – presumably because they had no non-system dependencies. But iuplua53.dll required iup.dll and lua53.dll, and neither of these was on the PATH; nor were they in the current directory. So they weren’t found. And Dependencies didn’t pick it up because it apparently just looks in the same folder as the subject DLL when looking for dependent DLLs. Which is fine if the subject DLL is loaded by an executable in that folder, but not otherwise.
Anyway – my fault. Apologies once again.
Simon