Mario,
I run into this problem sometimes, specifically when the .prg with the error that causes the debugger to pop up from my error handler, is located in a non-current directory, which for me is typically in the .. directory where the common code is stored. The only thing you can do is end VFP and restart it.
>Occasionnaly, when a prg contains an error, it seems to stay opened even if I cancel, close all, clear all, set proc to...
>
>The only way I found is to close and re-start VFP.