>Of course it does depend on what is open at the time....
>The trouble is that clicking on the button is producing events and these events can overlap each other (re-entrance). So if you click the button for times in a row, your function can start running AGAIN before the first instance has finished, so if the table were opened exclusively in the first instance of the function, to try to open it again (in the second instance) produces an error.
>
>Click slower, and you only ever have one instance at a time.

Hi William,
As I explained in the original post there were only two files involved: the main file that the form navigates, and a lookup file.
You suggest that the lookup function opens the lookup table exclusively - that is, it depends on how the table is open, not on what else is open at the time.
Your scenario may be an explanation for getting errors when clicking quickly, unfortunately, it does not apply to this case. The code that I posted creates a session object, and, in my tests, for the new session set exclusive was always off. On the other hand, in our system, the lookup file in question is always open by some users or unattended applications, so every attempt to open it exclusively will fail.

Thank you,
dz