RPC error is generally corrected by repairing the avast installation.
Control Panel > Add/Remove programs applet > avast antivirus
Choose Change/Remove button and then at the window that pop up, choose 'Repair' function at left.
If it does not succeed, try uninstall/boot/install/boot again.
Can you post the results?
Btw, do you have any other antivirus installed in your computer?