Since yesterday I got a strange Outlook Express message.

"To free up disk space outlook express can compact messages"

I call it strange as I don't have OE installed, because I'm using Outlook.

So looking around in my system to see if there was some OE instance somewhere I didn't find anything.  Googling for this problem gave me the solution.
The problem is with Windows Desktop Search.  it seems that by default OE is defined as an indexed location.  So there are three steps needed to solve this problem.

1) Close the message box with cancel
2) Click on the magnifying glass of Windows Desktop Search and choose Windows Desktop Search Options from the menu. You will see that OE is listed under "Included Locations". Click the modify button to bring up the "Indexed Locations popup".  Uncheck the Microsoft Outlook Express: Main Identity entry.
3) Open regedit and navigate to this key: HKEY_CURRENT_USER\Identities\{GUID}\Software\Microsoft\Outlo ok Express\5.0.  Replace GUID with the long number used for your identy.  I had only one GUID so it was easy. In the right pane double click on "Compact Check Count" and set the value to zero. Close regedit en restart your computer.

It solved the problem for me.  But I saw the counter was going up again.  So maybe in e few months I got the message again.  We will see.