So we now know that it is a problem with that particular machine.
Can you try it on the sockets that one of the other computers is using............swap them over........I have known a faulty socket cause this sort of thing............you know, a little vibration or whatever. I do not think that this actually is the problem but I am afraid that we are going to have to "chip away at the boulder" on this one and eliminate things one at a time.
It is now very late here so I will have another go later in the day.
PS I think that we have made some progress?