A customer had a problem that a virusscanner didn’t like a executable on the desktop and therefore somehow refused access to the user’s profile. The user decided to remove his profile (all the files in c:\users\<user>) and tried to logon. The user noticed that each time a temporary profile was created.
The solution was as follows :
Open regedit and go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
When you click on a SID you see which user this is.
As you notice, there are 2 identifiers. One with the extension .bak and one without. Remove the one without the .bak and remove the .bak extension from the other.
Now my customer was able to login with a clean profile.