>Any other things like this to look for, for accidentally closing a table when it should still be open?

If you see in the IDE, too, the easiest is to put USED("alias") in the Watch window and set a breakpoint. If you're not seeing it and have to rely on what happens at runtime, you might add some logging to the form that throws LIST STAT TO FILE periodically. I assume your error log already lists what tables are open when the error occurs; if not, add that.

Tamar