The latest update of Avast made a problem for me at work when it updated to the latest 2014 version. Suddenly networked computers were not able to communicate, could not ping them by IP or netBIOS name, host unreachable, timeouts etc.
After spending a couple hours changing every setting I could find in the Avast firewall, nothing would allow communications. Resetting winsock, flushing caches, DNS, ARP table, recycled the router even, nothing worked!
Finally found a solution that worked for us. The only way I could get communications back was by uninstalling and reinstalling via the latest Avast installer (not going through update channel again). After uninstalling, do turn OFF the Windows firewall as it’s possible that having it on during install triggers the problem as well. I cannot confirm this but it did happen on one workstation the reinstall did not work. After uninstalling the firewall module, shutting off Windows firewall, then reinstalling Avast firewall module the second time, it worked.
I hope this helps. Again, just try uninstalling the firewall module, turn off Windows firewall, reinstall Avast firewall module, and see if that doesn’t fix it. Let me know!