Weird, we have this kind of software (for shipbuilding), we release some COM objects to our clients, and open up some API's for them to perform data mining and extractions, or a customize application needed on their side. first they write it in C# however, found the performance is terribly slow. we write it under VB, and never experience any problem regarding registering classes/services through dispatching it in Python, C++ and VB (though not tried but some of my co-workers do). I'm still new to .NET and keeping myself to get familiarize with COM+ Interop, hoping a new solution for them, but for the meantime... happy to provide by Python, and VBA for reports. fast and easy.