OK, now I see what you're talking about. The behavior I'm seeing it that I'm getting the error "Program - testparent undefined" each time I build, and then it adds yet another instance of Testparent to the project. So far, I'm up to 4 of them showing up at once! I'm reporting this one as a bug to MS.

I've also figured out how you can fix this. First, you need to take the path specification out of your class definition in TestChild. I would think that if you SET PATH to the libs directory that would be all you have to do, but I found that VFP still doesn't know where to look for TestParent.prg. When you build, you can click the Locate button when it says it can't find TestParent.prg and point it to the TestParent.prg in the libs directory. It shouldn't ask you again, and subsequent builds won't create duplicates in your project.