Jack,
David is right, it's a bug in the debugger. If it kicks up in a .prg file that is not in the current directory a file handle gets stuck. Quiting VFP is the only way to clear it. Until you get the .prg debugged move it to the current directory, then move it back once it's running ok.
>Sometimes when I compile a prg I get: cannot create prgname.fxp. Anyone know how to clear this without restarting vfp ???