The User Profile Service failed the logon. User profile cannot be loaded

Error message when you log on to a Windows Vista-based or Windows 7-based computer by using a temporary profile: "The User Profile Service failed the logon. User profile cannot be loaded"

Possible causes:

1. This issue may occur if the user profile was manually deleted by using the command prompt or Windows Explorer by a user or by some program. A profile that is manually deleted does not remove the security identifier (SID) from the user profile list in the registry. Since the SID is still present, Vista will still try to load the profile by using the ProfileImagePath that points to a nonexistent path. Therefore, the profile cannot be loaded.
2. This can also be a issue with the user profile entering into a backup state.
3. Manually renaming the C:\Users\(User Name) folder.

To resolve this problem yourself, follow these steps:

1. Delete the profile by using the Computer Properties dialog box. To do this, follow these steps:
• Click Start, right-click Computer, and then click Properties.
• Click Change settings.
• In the System Properties dialog box, click the Advanced tab.
• Under User Profiles, click Settings.
• In the User Profiles dialog box, select the profile that you want to delete, click Delete, and then click OK.
2. Click Start, type regedit in the Start search box, and then press ENTER.
3. Locate and then expand the following registry subkey:
   
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
4. Right-click the SID that you want to remove, and then click Delete.
5. Log on to the computer and create a new profile.

Source: http://support.microsoft.com/kb/947215