I'm having the exact same problem ever since I've upgraded to 7.0.1466. Avast shuts down frequently without any notice whatsoever. The event viewer gives me messages like this one:
"The avast! Antivirus service terminated unexpectedly. It has done this 1 time(s). The following corrective action will be taken in 5000 milliseconds: Restart the service."
Usually, this happens 3 times in a row, with the result that there is no restart after the third time. The real bad thing is that there is no way of knowing, except when I actually open avast. I can then click "Fix it", and it will actually restart (until it crashes again, of course).
I followed the advice given above, uninstalled, booted into safe mode, ran the uninst utility, and then reinstalled. No difference. It keeps doing it.
The only obvious thing I've noticed is that I sometimes see a new avast icon on top of the startup screen when I start Outlook 2010, and sometimes I don't.
I have a pretty plain system, Win7 Ultimate 64bit, Windows firewall, Windows Defender, thats it. No other security software was ever installed (except previous versions of avast.).
Obviously this is a major risk as the system is completely unprotected at times without me knowing. For the time being, I'll go back to the previous version.
Any idea anybody? Thanks a lot.