I cannot see a plugin for Outlook 2003 with Avast 6. Should there be one?
I have no solution to your problem, but I am experiencing something similar. We are running XP Pro and updated to Avast 6; since then my email has worked all right, but other accounts on the same computer receive the error message “The add-in ‘C:\Program Files\Alwil Software\Avast5\ashOutXt.dll’ could not be installed or loaded.” I have looked at the various solutions for this in previous versions of Avast, but to no avail. The registry has the correct information (although I note that there is still a stray folder in the Program Files for the older Alwil Software). There are no plugins to disable. It is frustrating, because prior to the update we were experiencing no problems. It would be nice if someone would respond.
Outlook 2003 → Help → About → Disabled items?