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>But now the challenge is to make that same dll work from VFP and I ran into the same problem - it doesn't find that .ini file. Since I can not test that DLL from VFP, I am not sure where to place that .ini file and how to name it. I sent this question to my colleague who developed that class.

Sure you can (assuming you have the source to the .NET DLL). Open the .NET project up, select Debug, then Attach to process. Find the VFP instance and attach to it. Now you can set your breakpoints in the .NET code and they will be hit when your VFP code calls it.