>If you have an existing form, and the tables aren't located in the same relative path as when they were added to the DE, then, when you open the form you'll have a chance to locate the files.
>
>If you don't locate the files, and instead ignore the warning, and continue to open the form and save it, the DE will be saved w/o the tables it could not find.
>
>>Are the tables in a different location from where they were when the form was created?

>>Yes.
>>
>>Problem is, I think, in saving form. Cause after one "mistical" saving all tables in DataEnviropment dissappear. Without any warning.

That's the sure way to delete some tables from the DE. But sometimes it happens with form which was open dozen times before that. I've noticed that it happened when I ran the form from the designer. I stopped doing that, and it never happened again. Then I began doing it again, and it also didn't happen again. Maybe the wind changed?