RHEL 5 & NFS Input/Output Error

[Ryan Golhar]

Interstingly enough, I'm seeing the same thing - I have a RHEL 5 NFS 
server running and a bunch of RHEL 3 workstations mounting user home 
directories from the RHEL 5 server.

I can ssh into the workstations but creating files gives the same 
Input/Output error.  The server hard drives are fine BUT I do see this 
in /var/log/messages on every occurrence on the clients:

  kernel: svc: unknown version (3)

I'm not able to log into the clients from the GUI so something serious 
is going on.