Thanks for posting back. It seemed you already had solved the problem via fixing the list of errors you got from Mike's whichone.
I can give you another thing to do in the future: Before BUILD, open the debugger, especially the Debug Output window, then build. VFP will then do a verbose listing of things he does during compiling. If VFP does not spit out errors you will at least see on which file vfp stopped compiling.
Also, as you say the error is reported about an APP file: If you compile a project to an exe or dll, at first foxpro genereates an APP always and then adds something making it a DLL or EXE and changes file extension. If that fails the problem could be as simple as the EXE was still in memory, started. Or it was readonly. Simply delete the old EXE or DLL before BUILD and that should go away.
Bye, Olaf.