Try the following:
1_ download
http://public.avast.com/~kurtin/part-setup_ais-570.vpx2_ Set program updates and definitions updates to "manual" (both of them).
3_ settings -> troubleshooting -> disable self defense module.
4_ copy the above vpx file in your
c:\Program Files\Avast Software\avast*\Setup\part-setup_ais-570.vpx
(note I used "*" in case you have some number in that folder name).
5_ perform program update.
6_ wait for the program update to finish and reboot.
7_ reset the program update settings to "ask" and the definition updates to "auto"
8_ re-enable the self defense module.
Please report back.