I've tried the latest version you suggested but unfortunately I get the same result. I've attached 2 screenshots, one with the exception message and the other with the location of the exception. I don't know if these are helpful.
I've tried also to call my COM Object using late binding but got the same result so I guess that rules out any issues with the type library. Is it possible for someone over there to try to create a test application in another Win32 language (not .NET), like C++ or VB and try use my COM object and see if anything happens?
Happy New Year :)