1. Quit Outlook 2003.
  2. Click Start, click Run, type regedit in the Open box, and then click OK.
  3. Expand the registry, and then click to select the following subkey:
    HKEY_LOCAL_MACHINE\Software\Microsoft\Exchange\Client\Extensions
  4. Right-click Exchange Extensions, and then click Delete.
  5. Click Yes to confirm the deletion of the Exchange Extensions string value.
  6. On the File menu, click Exit to quit Registry Editor.