RPC error is generally related to other antivirus present or, at least, firewall blocking. RPC error may also be because of avast! services being stopped.
Anyway, RPC error is most likely correct by this procedure:
Go to Control Panel > Add/Remove programs > avast! antivirus > Remove
Then choose Repair function in the pop up window (Repair).
If this does not help, can you uninstall / boot / install / boot again?