NFS random "permission denied"

[Dan Wade <dan.wade@kcl.ac.uk>]

Hi -

Forty NFS client workstations running Debian etch and sarge, am-utils
automounter, a dozen active users.  Server is Debian sarge on Dell
PowerEdge 2850, PERC, Raid-5, stock kernel 2.6.8-2-686-smp.  Runs just
fine for about 3 months, then starts randomly saying "permission
denied".  nfs-kernel-server restart doesn't fix it.  Reboot has worked
on both of two occasions, but 3 months later it starts "permission
denied" again.  If there's an error in /etc/exports, I can't see it.

Googling found a couple of similar reports, but no obvious course of
action other than checking /etc/exports.  If I've got an error there, I
can't see it.  Sorry, can't publish - security.  In any case the
symptoms don't mesh with a syntax error.  What should I do?

- Dan