NFS Portmap: RPC: Program not registered... all of a sudden?

["Christopher C. Stevenson" <csteven@xxxxxxxxxxxxxxxxxxxxx>]

An urgent request of this kind community-

All of a sudden, two our our Tru64 boxes have decided they won't listen to
each other's NFS requests, whereas in the past they've been very happy.  
Initially I checked for daemons rpc.statd, rpc.lockd, mountd, etc., then
restarted nfs and nfsmount in /sbin/init.d by hand on each, then went so
far as to reboot each... no dice.  Each box is happily exporting and
mounting disks to half a dozen other machines in the same environment, but
have decided to shut each other out. Showmount -e from one box, querying
the other, produces the same RPC: Program unregistered errors.

Any quick suggestions?  One of these boxes could be considered a central
disk server for our little UNIX research group ('brigus'), and it exports
a dozen-odd disks.  Only the machine 'wessex', a satellite DS10 (one of
several, the others reporting on problems) cannot pick them up.  I have
changed *nothing* on the machines in question.

Chris

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Christopher C Stevenson,  C4063                 office: (709) 737-2624
Dept. of Physics & Physical Oceanography        fax:    (709) 737-8739
Memorial University of Newfoundland		
St. John's, Newfoundland, CANADA  A1B 3X7
URL: http://www.physics.mun.ca/~csteven
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"We are all in the gutter, but some of us are looking at the stars."
                        -- Oscar Wilde