Permissions should be good, as I said I have been working on this for a while now with no problems before. And I have no problem saving PLN and I just tried a different LBK and that was ok too.
It would be nice to be able to save this file as we're ready to issue the drawings.
Also tried Save As with different name, still no good.
Tried that, got a "disk full" message, which is hard to believe as we have just had our server upgraded to 4x80Gb hard drives (from 1x40Gb). Am onto our computer consultants.
Apparently There was a quota mangement system in place, and I had reached my quota (does that mean I can go home for the rest of the day? I think not) so the problem was with our server setup (by others!)