This forum is for Microsoft Security Essentials only.
But, try this:
For popup choose no, or Outlook Express will failed to compact, known issue, likely will not get fixed
Open Outlook Express make sure working offline, if not double click computer icon lower bottom. Then go to file> folder> choose compact or compact all folders. Wait until Outlook Express is finished. Reopen Outlook Express and make sure to double click to be working online again if working offline (always connected to the internet connection). Repeat instructions each time Outlook Express ask again, it will in time, it’s normal.
Knightsky