To stop the error message,
right-click the magnifying glass icon in the main Windows tool bar,
and from the popup menu, choose “Windows Desktop Search Option.”
Look under “Included Locations” for an entry for Outlook Express.
Select it, and click the “Modify” button.
From the “Indexed Locations” popup, uncheck the Outlook Express entry
(or entries, if more than one).
Back out of all the dialogs, and the message should be gone.