Security software or a corrupt profile are the two most common reasons for this.
Some security software will try and scan the NTUSER.dat file in your profile when you login. This can keep the file locked and cause this message, or the same file is corrupt.
For the latter you'd need to login with an administrator account (can't be the account your having problems with) and rename the affected user profile directory in C:\Users. You can just add a .old to the name.
Then go in the registry and locate the following key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
Under this key you will see several keys with name like S-1-5.
- Select each key that starts with S-1-5-21 and look at the...