Solution

First, use Windows Update to be sure that all Windows components (including "RPC") is up to date. Then restart your computer and check if the problem persists. If it persists, follow these instructions:

   1. Right-click the icon MY COMPUTER and select MANAGE.
   2. In left column unroll SERVICES AND APPLICATIONS.
   3. Click on SERVICES.
   4. In the right column, look at the state of service avast! Antivirus.
   5. If the service isn't set to start automatically, set it that way (right-click it and select PROPERTIES and the STARTUP TYPE set to AUTOMATIC). Restart the computer after making the change.
   6. If it was already set to "Automatic", check the status of the service. If it not "Started", try to start it (right-click it and select START).
   7. If the service cannot be started, your avast! installation might be corrupted.
      Try repairing the avast! installation: click START -> CONTROL PANEL -> ADD/REMOVE PROGRAMS -> avast! Antivirus -> CHANGE/REMOVE and select REPAIR.