When it pops up the illegal operation box, click details. If it says "MSIMN caused an invalid page fault in module Msoe.dll at address.", then it can be because the attributes of any or all of the Outlook Express .dbx mail files are set to read only.
1. Click Start, point to Find, and then click Files or Folders.
2. In the Named box, type *.dbx, in the Look in box, click Local hard drives (C
, and then click Find Now.
3. For each *.dbx file that is found, right-click the file, click Properties, and then clear the Read-only check box.
4. Click Apply, and then click Close.