Invalid Drive Specification when logging into NetWare 5.1

We are running NetWare 5.1 with Windows 98 and XP clients. When the XP
clients login, they are getting an invalid drive specification. So when
they try to access a certain network app it won’t run. What seems to get
them around it for now is if i re-logon to NetWare, it then picks the
mappings up. Does anyone have any ideas on this or where I should look?
Thanks!