Do you have any other antivirus installed in your computer?
Did you have in the past? Which one?
This could be related to a RPC error which is due to other antivirus present or, at least, firewall blocking. Do you use an third party firewall? Which one?

If you already tried to repair your installation (Control Panel > Add/Remove programs > avast! antivirus > Remove … Repair function) I can only suggest that you disable Windows Firewall > uninstall avast > boot > install > boot again > enable Windows firewall…