Losing mappings to remote sever

We are running Netware 6.X and are attaching with Win98, Win2k and WinXP. Sometimes they can login and get the mappings, but they lose the mappings after about 30 minutes. Or, they won’t pickup the mappings at all. They have the latest client installed. The win98 computers seems to do better than the W2k or XP computers. They login to the local server with no problems. It is just the remote server that they map to that has the problem. I have checked other resources and tryed their suggestions with no luck.

Does anyone have any suggest that might work?

Thanks in advance.
Russ