Trying to debug from C# into VB6 yields TYPE_E_CANTLOADLIBRARY?

I have a VB6 DLL being accessed from some C# code.

Using the compiled & registered VB6 DLL there is no problem. But when I load the VB6 source into the VB6 IDE and run the project, the next run of the C# code will fail with the error below.

Stopping the running DLL in the VB6 IDE will again allow the C# program to work from the compiled DLL.

The VB6 DLL is compiled with binary compatibility.

The error message I receive in C# is:

An unhandled exception of type 'System.InvalidCastException' occurred in appname.exe Additional information:

Unable to cast COM object of type 'dllname.classnameClass' to interface type 'dllname._classname'.

This operation failed because the QueryInterface call on the COM component for the interface with IID '{D8AB6D65-F5E7-4B9C-A039-67DDC630E5F7}' failed due to the following error:

Error loading type library/DLL. (Exception from HRESULT: 0x80029C4A (TYPE_E_CANTLOADLIBRARY)).

Specifically this error occurs when the C# code tries to access any part of the interop object which actually comes from the underlying COM object. But accessing .NET Object-derived things like .ToString() work fine on that object.

Why am I getting this error?

Furthermore:

If I compile the C# code when the VB6 code is NOT running, it builds fine. But compiling when the VB6 code IS running, then I get an error:

BC30002 dllname.classname is not defined.

Thanks

Maybe someone else will have a deeper understanding, but this is what I eventually figured out:

• Running either Visual Studio (.NET) or Visual Basic 6 as ADMIN while debugging in this scenario would cause the error. Running BOTH as WITHOUT ADMIN rights then it would work.

The quandary is that admin rights are needed for certain build operations (specifically, registering COM DLLs automatically). So that was the pitfall; ultimately I had to repeatedly switch between admin/non-admin settings for both tools in order to code-test-modify...

Note - when I've debugged in a different scenario where the program is a VB6 EXE debugging into C# code, this was never a problem. Everything could run in as admin no problem.