“An attempt was made to load a program with an incorrect format” even when the platforms are the same

I’m calling functions from a 32-bit unmanaged DLL on a 64-bit system. What I get is:

BadImageFormatException: An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)

At first, I had my projects set to the Any CPU platform, so I changed them both to x86, but this error is still occurring. That’s really the only fix I know for this.

The DLLs aren’t corrupt or anything, because I can use them with other programs (that I don’t have the source to). I thought that perhaps it wasn’t finding a dependency, but I checked and they’re all there. Plus, wouldn’t it throw a DllNotFoundException in that case?

What else can I do? And before you say “Use a 64-bit unmanaged DLL instead,” let me point out that there isn’t one. 😉

If you try to run 32-bit applications on IIS 7 (and/or 64-bit OS machine), you will get the same error. So, from the IIS 7, right click on the applications’ application pool and go to “advanced settings” and change “Enable 32-Bit Applications” to “TRUE”.

Restart your website and it should work.