Tip of the day: “An attempt was made to load a program with an incorrect format” .NET P/INVOKE issue

The other day I was using a 3rd party utility which was built on the .NET platform. My primary work computer happens to be a x64 installation. So on this computer when I fired the utility up, and tried to perform some tasks it would error with a .NET Exception which basically had the following characteristics:

– Message: “An attempt was made to load a program with an incorrect format”

– Exception: System.BadImageFormatException

After some troubleshooting it turned out that this utility was trying to load a plain-old DLL (which exported some functions) presumably using P/Invoke. The DLL was built for 32-bit platforms. Now it turns out that by design a 64-bit process (the 3rd party utility would run as a 64-bit process owing to the 64-bit .NET runtime) would be prevented from loading a non-COM 32-bit DLL (32-bit COM DLLs are loaded in a DLLHOST.EXE surrogate when invoked from a 64-bit client process, BTW…) with the above exception.

To configure the utility to run as a 32-bit .NET process, it turns out you can use the CORFLAGS utility. You run it as follows to switch the 32-bit execution mode ON:

corflags utility.exe /32Bit+

To turn it off, just use /32Bit- in the above command line.