hmmmm.... ok, the picture is a little more clearer now. Have you thought about dumping Access in favor something that is more multi-user friendly. Like SQL Server, Oracle or even MySQL. It sounds like you've exceeded the limits of Access, which is file based, and hitting it as often as you are (every client, every 5 seconds) it's going to get corrupted fairly quick. You may want to go with something more server oriented that scales better.

-tg