I had the same issue, after the update, when starting the PC it would sometimes "freeze" in a screen with only the mouse pointer and the taskbar. Fortunately it seems to have been fixed by the following update that came in the next days.
I want to say I'm quite unhappy with avast! in this subject, it seems it isn't the best one in the quality assurance needed to rollout updates. People got BSODs, this is very weird for a security software programmer to let happen! You need to test it more before making the software update available...