C# ActiveX dll fails on Win7 x64 in VS Release but not Debug

I have several vendor supplied DLLs for talking to a Signature Capture Device. We build our C# windows app platform target set to "any cpu" on an XP x86 machine. When the application is run on Win7 32 bits computer it works fine. When it is run on Win7 64bit computer it fails.

Running the Visual Studio 2010 debugger on Win 7 x64 in "Debug mode" works fine. Running in Release mode on Win7 x64 fails.

I can change the platform to target x64 then Release mode works fine on Win7 x64, but this is not a viable solution. There are 1200 XP machines in the field and newer machines going out are Win7 x64.

I see many questions and answers about targeting a 32 bit dll from a 64 bit machine. This problem seems rather unique and inexplicable as "any cpu" is supposed to run on Win7 x64. I guess I need help determining if the problem is with the dlls or the ActiveX Com Bridge, and what options can be used to build for x86 and be able to run on x64.

Thank you in advance!