Check to see if your firewall (FW) is blocking anything related to Avast.
If it is not related to your FW and you are still having the problem, you can try a repair of Avast:
- Go to Control Panel > Add/Remove programs > Avast Antivirus.
- Scroll down and choose Repair function in the pop-up window.
- Reboot.
Is this a constant problem or this just happened once? Was this after getting an Avast update? As stated earlier, these things do happen on occasion, and often times a simple reboot is all that is needed. But let us know the answers to the above questions so we can help you more. Thank you.