Just to officially close this thread it turned out to be a virus scan by McAfee. Moral of the story is, never trust the IT department. I asked them about this scan on day 1 as it was my first thought. They swore blind it was not the problem. You live and learn!
Turns out that they had installed McAfee on a number of laptops locally, these then temporarily locked the database files when connected to the network during a scan. Of course, the first person to savework whilst the db was locked caused a knock-on dabacon error effect.
