You may still be infected with Nimba or have damaged RICHED20.DLL file.

A few months back when I was helping an aquaintance with some computer problems he was experiencing I had my first run in with the nimba virus. He was getting "out of memory" errors when trying to send email with Outlook. It didn't take me long to download an antivirus program and figure out that he had been infected with Nimba.

Nimba is notoriously difficult to remove. Check for a file named wininit.ini and delete it. Look for a line in your SYSTEM.INI that starts with SHELL. if it says anything other than "shell=explorer.exe" then you may still be infected.

Nimba affects the RichEd20.DLL. This file may need to be restored from the original Outlook/Office install CDs. Check out this article on Symantecs site...

NIMBA

Good Luck