XP shared network drive disapear

Does anyone have an idea how to stop XP Pro from dropping network share drives. I have a few XP Pro workstations that at least once a day drop the network share drive. This has be going on for two years now. We have Windows 2000 server with 10 useres. One of the users PC just dropes the shared drive for no reason. I have to go back and remap the drive all the time. I have tried several fixes from Microsoft and the Experts Exchange and still is doing the same thing. Changed the time out for the share in the registry for both the server and the XP work station. Nothing has helped so far.