This sometimes happens on Windows 7 and Windows 2008 after a profile is deleted. The solution:
1) login to the box as an administrator
2) open regedit and navigate to:
3) expand ProfileList so that you can see a list of SIDS of loaded user profiles
4) click on each SID in turn and look at the ProfileImagePath value to determine which user profile the SID belongs to
NOTE: You can at this point simply delete the profile however you will loose the data. This is the only option at the time of this post which I have tested. Step 5 below may avoid this! But I havent tested it.
5) add .old to any SIDs (including ones ending with .bak!!! - i.e. .bak becomes .bak.old ) belonging to the user profile that keeps logging in on a TEMP user profile
7) now login as the user and you should log in as that user now