Back up the files in the OE data folder. The folder can be found by going to Tools > Options > Maintenance > Store Folder.
1. Register two important Outlook files. Go to Start > Run and type regsvr32 OLE32.DLL
Also, type regsvr32 inetcomm.dll
2. Register Outlook Express.
Click Start, and then click Run. In the Open box, type msimn /reg, and then click OK.
(Note that you will not see anything happen.)
In Internet Explorer click Options on the Tools menu.
Click the Programs tab and select Outlook Express as the default e-mail client and as the default news client. You can change those later if you wish.
3. Check if folders.dbx file is corrupt. With OE close, do search for folders.dbx and rename it to folders.old.
The file is located in C:\Documents and Settings\<account name>\Local Settings\Application Data\Identities\<hexadecimal number>\Microsoft\Outlook Express folder. It is a hidden folder, so you have to unhide hidden folders and files to see it. Go to any folder and select Tools > Folders Options > View. Check "Show hidden files and folders". Click OK.
4. Create a new Outlook Express identity.
5. Repair or Reinstall Outlook Express.
Hope this helps!