nfs hangs on NetApp NAS device

[Betsie Spann]

My RH AS 3.0 system frequently hangs with the message   "nfs: server pafiler not 
responding"
It's a NetApp NAS device that is ro nfs mounted by the entire universe here.  My Linux 
guest frequently waits on it.  Then it has to be rebooted.  Network restarts hang on 
the server also.
I am using NFS vers 3 with a timeo value of 40 and rsize/wsize of 8192 using UDP.   
I'm going to try the tcp option next.  
Any suggestions or known problems, please?
Betsie