kernel: nfs: server not responding,timed out

Hi

We are running RedHat 6.2 on several high end machines in New Zealand,
at the MetService.  The reason for running 6.2 is that the model we use
to run weather reports, only works (at the moment) on the 6.2 kernel. 
We have slightly tweaked all our kernels to 2.2.17-14smp.

We get errors occasionally, which occer when a machine called "ajax"
tries to read a file on a readonly nfs share on a machine called "lisa".
 The job we have running, reads multiple files from this read only nfs
share.  Something goes wrong, and when this job reads a file from the
share, it reports that it cannot find the file, and carries on with the
next file in the job list, from the same nfs share, without a problem. 
This would seem that the nfs share temporarily times out, which results
in the following message appearing in /var/log/messages:

Sep 16 18:00:58 ajax kernel: nfs: server lisa.met.co.nz not responding,
timed out 
Sep 16 19:01:15 ajax kernel: nfs: server lisa.met.co.nz not responding,
timed out 

So ajax tries to read from lisa via nfs, cant find the file, our program
generates an error saying the file doesnt exist (when it clearly does),
and the above entry is added to the messages file on ajax.

Any help, or suggestions on extra settings to set on the nfs share to
avoid this problem would be greatly appreciated.  I have searched around
the net for similar problems, and found this thread, which matches my
problem as close as I can find:

http://www.redhat.com/mailing-lists/seawolf-list/msg32253.html

Thank you very much in advance,

Kind regards,
Dan Haines

Systems Administrator
MetService,
New Zealand.