A favourite topic for VB6 programmers! Adding a reference to a COM component in Visual Studio adds a reference to a specific version of the VB6 component, so rebuilding the VB6 component without binary compatibility will break the .NET project (you’ll have to re-add the reference to fix it). Switching on binary compatibility in the VB6 project will bring its own set of problems, so a better solution for an automated build would be to run TlbImp on your VB6 dll in your .NET project’s Pre-build event.

I just discovered that TheServerSide.NET has a free book available covering all of the intricacies of .NET to COM interop , so if you want to delve any further take a look here: COM and .NET Interoperability.