Thats not an uncommon glitch. Most typically, the cause is a damaged Deleted Items folder. Try, with Outlook Express
NOT RUNNING, going to:
C:\Documents and Settings\<Your User Name>\Local Settings\Application Data\Identities\{<Long Random Key String Here>}\Microsoft\Outlook Express.
Locate
Deleted Items.dbx, delete it, exit back to your desktop, launch Outlook Express, and see what happens. When OE is launched, Windows should rebuild the .dbx file you deleted.
If that doesn't do the trick, with Outlook Express
NOT RUNNING, navigate back to:
C:\Documents and Settings\<Your User Name>\Local Settings\Application Data\Identities\{<Long Random Key String Here>}\Microsoft\Outlook Express
Locate
Folders.dbx, delete it, exit back to your desktop, launch OE, and see what happens. You prolly will need to reset your OE preferences after doing either of these.
A good article on Outlook Express glitches and fixes can be found at Microsoft:
An Outlook Express basic repair kit, with a related article,
The Other E-Mail Threat: File Corruption in Outlook Express offering more troubleshooting tips and techniques. Another useful resource is the MVP website of the author of those 2 articles, Tom Koch's
Inside Outlook Express