Why do I get "Bad Calling Convention" when trying to call my VC++ dll from VB?

Visual Basic only supports calling functions in Dlls that are declared with the __stdcall calling convention. This is different from the default convention in VC++,  __cdecl, which stands for "C' calling convention. The two are not the same (but that's another topic) and are not interchangeable. The solution? make sure you declare your dll's functions as __stdcall.