Any CPU

Could not load file or assembly '<name>' or one of its dependencies. An attempt was made to load a program with an incorrect format.

Ran into the above error, found this post.  Changed from x86 to Any CPU, and it worked!

QuickBooks SDK 8.0, QBFC8 and Windows Server 64 Bit

Was having problems with QB SDK 8.0 not working properly, discovered via intuit developer forum that I needed to force x86 compilation instead of "Any CPU".  Was getting an error similar to "Could not find the COM Class with CLSID *****-******....".  Switched the compilation method to x86 explicitly, and it started working.  Yay!