I have 600+ users in AD, but only one causes me trouble. The problem is I can reset his password from AD, he can then log in to his machine. After that he would like to change his password from Windows 7, and proceeds without errors. Logs out or locks the workstation but cannot access it again using either old or new password. So I have to reset it again and he can only use the one I provide for him. All our machines are in the same physical location in the same subnet. Functional level is 2003.

I'm totally out of ideas. I could create him new user account, but I'd possibly like to know what causes this. I can only suspect some sort of synchronisation problems but other accounts work fine, and I don't know how to dig deeper into this.

Thanks, Piotr