Cannot get Mapings

I am running mix mode W2k & NT 40 (sp6) servers. The users data folders are on the NT40 server. On certain machine Users can log onto the domain, ping all servers (by IP and name) but cannot map to the NT40 server(msg access denied). If I take thosesame users log onto another machine they can map to the NT40 server. The users workstations are running W2K.