Strange… Is there any other security program that could be interfering?
Firewall? HIPS protection?
It could sound stupid, but can’t you try an installation from the scratch:

  1. Uninstall avast from Control Panel first.
  2. Boot.
  3. Use Avast Uninstall for complete uninstallation.
  4. Boot.
  5. Install again the last version.
  6. Boot.
  7. Check and post the results.