C# program and C++ DLL compiled for 32-bit system crash on 64-bit system

I have a C# application that makes use of a DLL as I need C++ to access some unmanaged functionalities of the user32 API (I cannot use PInvoke for that). I compile both the application and the DLL for x86 architectures, and everything works fine on Windows 7 32 bits. Now the problem is, on Windows 7 64 bits, the application crashes when I t开发者_JAVA百科ry to use the feature that relies on the DLL (but all the rest works fine).

I suspect that this is a 32/64 bits issue, so I tried re-compiling the DLL for x64 architectures, and now I can choose at runtime which DLL to load between the x86 and the x64. But it still crashes when I try to use the feature that relies on the DLL (which makes sense as I try to load a 64-bit DLL into a 32-bit program). I haven't tried yet to compile both the application and the DLL for x64. I suspect it would work, however it would require me to have two different installers, and I don't want to go there. Any clue?

When interoping with unmanaged code, you need to ensure your .Net app runs on the same subsystem (32-bit or 64-bit). As you've stated the DLL you're loading is for x86, force the .Net to build for only the x86 platform. This setting is found in your project's properties, on the build tab. The default is any CPU, change the setting to x86 to match your unmanaged DLL and you should be fine regardless if you run on a 64-bit or 32-bit OS.