System.IO.FileNotFound Exception. Additional information: File or assembly name BLAH, or one of its dependencies, was not found.

This error is weird. It seems related to mixing unmanaged code with managed.

OK, i seem to have the beginnings of a solution.. You MUST use pointers when declaring unmanaged types. I am thinking i will need to do a proper managed C++ wrapper class. See: Part I: Introduction to Wrapping C++ Classes.

Clean/Rebuild is your friend.