Outlook XP (2002) startup error: "...requires Microsoft Outlook Express 4.01 or greater."

On a system running WinXP Pro w/ SP2 and Office XP. Attempts to open
Outlook result in the error message:

"Cannot start Microsoft Outlook. Outlook requires Microsoft Outlook
Express 4.01 or greater. You can install Outlook Express by running
IE5Setup.exe from the IE5 folder located on your CD or through Windows
Update website."


Outlook Express version 6 is installed and runs without error, though
it is not used. The version of Outlook installed is Outlook XP.

I have viewed and tried...

Outlook XP (2002) startup error: "...requires Microsoft Outlook Express 4.01 or greater."