Thanks Simonta - I think it will have to remain a 'mystery' and I'll just have to give it a minute or so before I go to 'User' in order to get a full tray. No group pol.
R.e allusers/ntuser.dat - I just don't know - I've had one since W2000 and others as per my link think it exists too. I've had a peek using Mr O's prog 'loadhive', and since it doesn't seem to be the 'culprit' anyway it matters not. I'll run HJT and see if there are any clues there.