Stefan's solution is the way to approach the situation. By trying to use the file exclusively, an error will occur if someone else has it open.
In the CATCH, you can do anything you want (you don't have to show a messagebox. Are you using VFP8, or something prior to that?
>I don't eant to know if the table lock or not, I want to know if the table open by any user in my network.
Steve Gibson