We have a Windows domain with about 60 user accounts. Sometimes when a user logs in to his computer (already his account is created and has files there) windows logs him to a temporary user, displaying his name and everything, but without his files and data. This problem is rare and is solved simply by logging out and logging in. I noticed that it occurs at a close timings; they all happen at the same day if they did. My question is why does that happen? I want to trace the problem because it is so annoying when it happens, and I can't find a relative event that may be causing it: no server is down when it happens, no system maintenance or anything.

We're running Windows Server 2003 R2 Standard, SP2 in the Domain Controller (and the same for the additional DC). The machines where this problem happened before are running Windows XP and Windows 7.