I don’t know if this will help, but it might.
First I must make it clear that I am no geek or guru - just an average somewhat electronically-challenged PC user.
That said, I am trying to help my elderly mother with her PC which had to be rebuilt a couple of weeks ago due to bad capacitors on her previous motherboard. She has been using PCs since the early 1990’s, & is in her late ‘80s now, & is trying to deal with the transition from everything XP + Outlook Express to Windows 7 64-bit with MS Office, including Outlook, 2007, also from AVG to Avast! Free. My mother’s Outlook gives that “Outlook experienced a serious problem with the ‘avast!’ addin’ add-in...” notice every single time she opens her Outlook ’07 for about the last week or so.
I have MS Office 2003 Pro w/ Outlook ‘03 on my PC. (Yes, this is relevant to the current subject - you’ll see.) I have Avast! 7 Internet Security completely & auto-updating itself every 4 hours (now program 7.0.1456) & all shields turned on in my PC; and I have never seen the Outlook Anti-Spam bar in my Outlook ‘03. Both PCs had problems installing the latest Avast! program update. On both machines the summary kept saying it still needed the program to be updated but the maintenance section said it was already updated which was fixed by reboot on both machines.
I've got to wonder why I don't see the same “Outlook encountered.....” message every time I open my Outlook 2003.
There seems to be a close correlation between the Avast! add-ins and the issues both in this thread and some others in this forum:
forum.avast.com/index.php?topic=99503.0
forum.avast.com/index.php?topic=100692.msg804892
forum.avast.com/index.php?topic=101072, &
forum.avast.com/index.php?topic=70667.0 (of course with the “http://” in front).
It might help if the Avast! Team took a look at those other threads. Maybe it would help to look at this larger picture.