You could try uninstalling the firewall function.
From the Control Panel > Programs and Features, find avast and select avast Antivirus Now click the Uninstall/Change Button (or right click on the entry). From the new window, select the Change Option, you will see the various avast elements/shields that are installed. Uncheck the Firewall option and OK/Confirm your way out. You will probably be asked to reboot, if you aren't I would suggest that you do.
You can obviously reverse this process if in future you want to install the firewall element.