I did not suggest to do it every time. I mean, if there is something wrong with the environment, you need to delete FXPs/FOXUSER and restart VFP only once to fix the situation, then recompiling should work normal after that. I just had this situation this week, and recompiling/tracing works just fine since then.
If there is a need to restart VFP every time, then there is clearly something wrong with the environment.

>Thanks for your advise Nick, but your solution is more troublesome than closing and reopening the program. Besides, I have to close it anyway to delete this files, right?
>Anyway, what I'd like to know is What causes this error and how to avid it.
>
>Thanks for your reply.