To resolve this issue, remove the Identities key from the registry and then restart Outlook Express. To remove the Identities key, you must edit the registry.
WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
To resolve this issue:
In Outlook Express 5.5, back up the messages and addresses, and then export the Address Book.
Start Registry Editor (Regedit.exe).
Locate the following key in the registry:
HKEY_CURRENT_USER/Identities
On the Registry menu, click Export Registry File, and then click Desktop in the Save in box.
In the File Name box, type Identities, and then click Save.
In Registry Editor, right-click the Identities key, and then click Delete.
Quit Registry Editor.
Restart Outlook Express to make sure that the functionality has returned.
Import the items from the old identity.