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:
- Uninstall avast from Control Panel first.
- Boot.
- Use Avast Uninstall for complete uninstallation.
- Boot.
- Install again the last version.
- Boot.
- Check and post the results.