Well, actually, i have narrowed it down to a treeview control that doesn't work correctly on some computers (the node.click routine is not executed), wich in it's turn causes a query not to run. More the strange is that that on the specific form there are 2 treeview controls, and one works as a charm.
And remember, after installing vfp 7.0 and uninstalling it again (even wothout running it once), my problem is disappeared, without changing anything to my applications code or even recompiling this code. It seems i have another day of frustration ahead.

But, of course, thanks for your comments

Vincent