Actually, you shouldn't be running two AV programs at the same time. You should unistall Avast and just run the MS
Actually, I'm more inclined to keep Avast and uninstall MS. I've been using Avast for several years. MS inadvertently installed security essentials when I installed Win 7 a couple of weeks ago, or during the initial update process. Seems to work OK, but I prefer my tried-and-true approach.
What bothers me is that many of these programs have an "always running" component that interferes swith other similar programs. For example, I used to run Spybot S&D, Ad-Aware, and MS Defender, but I s-canned Ad-Aware and only ran defender for the occasional scan, keeping Spybot's program as the primary TSR for spyware and Avast as the primary AV program. There were some occasional compatibility issues when competing programs were seeking to serve the same purpose at the same time.