I’ve finally resolved the action center issue and the impossibility to make an Avast Config Backup with a really clean install and a registry cleaner by Ccleaner and a manual deletion of the avast’s folders in every folders of my pc.
But now I’ve another problem. I can’t install Ad Blocker in Firefox. Avast says that it is installed but Firefox don’t detect the plug-in. ??? How I can resolve this issue ?
Did you have Adblock add on installed on FF? If so, please uninstall it, then try to reinstall Avast Adblock from avast menu.
No I don’t have it…before the clean install I had only Avast AdBlocker and Avast Online Security Plug-ins
Hmm then try to uninstall it from the avast menu and reinstall avast adblock, and see if this would do the trick
I’ve already tried 3 or 4 times…but nothing change
see solution here: http://forum.avast.com/index.php?topic=124075.msg940953#msg940953
Thank you a lot for the solution!!! 
You’re welcome 