'RPC transaction timed out' error on clients

[Dr R D Gidden]

We are running 2.1.5 (old!!) on our school file server
and it has suddenly started giving errors to users logging 
on from Acorns with Omniclient I with the error shown on 
the client machine as in the Subject: line.  I believe 
Omniclient is a samba client (?)

PC's do not seem to be affected, nor do Acorns *already* 
logged on - "RPC communication failed on mount" for users 
wanting to log on afresh - I'm having to reboot the file 
server nearly as much as W95 ;-) as I have no idea which 
process on the file server is falling over - so that I 
might kill -1 <PID>.  ps -aux gives a reasonable looking 
list both before and after the happening.

Help gratefully received!

Bob.