1. Open the Registry Editor, by clicking Start (Windows Logo Pearl button), and then type
regedit then press Enter. (If you’re on Windows XP, click on Start -> Run.)
2. Navigate to: HKEY_CURRENT_USER\Software\Microsoft\MSNMessenger\PerPassportSettings
3. Look in each passport folder (if more than one) and locate the "UTL" string containing your email address. Delete it.
4. Close the Windows Registry Editor, and reboot your computer.
Source: Windows Live Solution Center
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