wandering drive

We are running SBS 4.5 on file server (fs1) and Windows 2000 server (Terminal Server) (ts1)on the terminal server.
“j” drive which is the apps off “c” drive ts1 keeps getting a red X on it have to log administrator off then on again to “reconnect” it is starting to happen more and more frequently
when it happens users loose MSOutlook,Word & Excel
dont know what to do now any help greatly appreciated
Mark White