Rick's Message has some good thoughts on the subject as well. I have had times where the path and/or duplicate .prg's have caused the problem. The trace window should at least tell you what program is running (you may need to check the calling program to make sure it's not a procedure within a program) and do a find for all programs with that name.
One last thing I forgot; are you running straight source code or do you have any .apps or .exe's runing. Those can easily get out of sync as well.