I'm glad you got it up and running. Could have been that the Business Contact Manager (was this an MS plugin for Outlook?) didn't play nicely with Avast.
I really wouldn't worry too much about the error you received prior to fixing this problem. As long as everything runs smoothly from here on out, you needn't really worry about it.
I've had certain programs wreak havoc with other programs and they would generate all kinds of strange errors as well as freezing certain apps., and trying to figure out what was going on would be a nightmare. Since you had recently reinstalled/upgraded the OS along with some other apps, it was hard for you to isolate the problem since you had a lot of changes over a short period of time.