If you are willing to test 6.0.945 here’s the link http://forum.avast.com/index.php?topic=70655.0
5.1.xxx did have some lingering glitches. Please don’t give up without at least trying 6.0.945 I have found it to be more stable than 5.1.xxx Avast has moved on to 6.0.xxx and are currently working out all the kinks before final release.