The fact that it is an MFC class it does mean that is written in standard C++.
MFC is as you know just a Microsoft set of packaged classes.
However, a DLL built from C++ may or may not conform to a "C" standard to pass variables to the client program and VFP is expecting "C" style I believe, not C++ style returns. Next week I'll probably dedicate myself to this problem and I hope to find a way ?
Thanks much !