>Is there a way to release this "Unknown" datasession after the form is released?

CLEAR ALL will do, but I doubt, you would want it in the real life application. It's better to find the reason for this behavior, though finding the reason could be a tough process. We had a similar problem 2 years ago, it turned out to be a MessageboxX function, which we used in VFP6 to simulate timed messagebox. That's why I'm asking for 3rd party tools/programs, etc.

What VFP version you're working in?