Thanks jpeachman! The solution to my problem was related to the Windows 2000 server config. I had the following Event Errors: 15, 534, 1000, 1053, 1789. Microsoft KB 262958 resolved them and the InGroup problem for me. I had actually printed this KB article off for our local computer shop for when they visited to look at the problem, but they went off on some other unsuccessful tangent. So I fixed it myself, what a waste of money on consultants! .... but I still don't know who, what or where the fault came from!