forget my last post here
I started a new thread about that and I later found out that
proxy settings changes are retained with Vista/Seven UAC off. So, disable UAC, reboot, change your proxy settings, re-enable UAC and reboot again.
ps: there's no actual "repair" function, that's just how we call the process of relaunching the setup process over an existing installation, and this can be done from the add/remove program panel (ie programs and features) Avast entry >>> either add/remove components from there, reinstall as is, or uninstall completely.