I just do not include the file extension and all works just fine. The OF ClassLib is always a PRG/FXP based file.

>I was eager to start using the new clause in VFP 7, "OF ClassLib" in PRG based classes. I went through much of the previously written PRG based classes, updating them like this:
>DEFINE CLASS deSD AS deIDSD OF deSD.PRG
>After doing this I could delete numerous SET PROCEDURE TO deSD.PRG ADDITIVE or similar statments. However, when I built an EXE, the parent classes weren't found. (Well, they were found when there was a path to them, but that doesn't count. They were in the EXE for heaven's sake!) After building a simple test exe and verifying that it was in fact a bug, I changed the syntax to DEFINE CLASS deSD AS deIDSD OF deSD.FXP and that worked. So at least until service pack 1 :-), you must use the FXP extension, not .PRG to show the lineage of your classes.