OK - cracked it! (With a pointer from someone in the FAH forums to look at the hosts file.)
Although this had an entry
127.0.0.1 localhost
it seems that was not enough. The machine is peter and the local domain is hillside - so amending the first line to
127.0.0.1 localhost localhost.localdomain localhost.hillside peter.hillside
has covered all eventualities - and smp is back on line. Shame about the 92% complete WU I lost though though.
So the uniprocesses have been restarted with the oneunit option to run them to completion, and all should be well again!
And interestingly - the whole machine is a WHOLE lot more responsive - opening a terminal window was taking 5 to 10 seconds - now it is instantaneous.
So - can anyone explain what the localhost setting does in multicore processors? Presumably it affects intercore pipes...
(Sorry for the delay in posting - I've been sufferening from a bad case of Manflu

)