Network goes down

I have a unix file & print server plus an NT 4.0 file and print server.
Twice in the last week the network has gone done — users can not access network resources, they can use the net logon. I’ve ended up making all the users shut down their pcs and then reboot both systems.
The only evidence I find is in the NT system event log:
event ID 2006, source: Srv
type: Error Computer: NT
The server received an incorretly formatted request from \\unixserver
and
event ID 3013, source: Rdr
type: warning, computer: NT
The redirector has timed out a request to NT.

Any idea what is going on?