I am posting here because the DNS FIltering forum has a grand total of 2 threads and no activity in several weeks.
Does the WebRoot DNS Filtering alter the TCP/IP v4 DNS properties of the client it's installed on? I have seen clients that are unable to access the internet, and on investigation found the TCP/IP v4 settings DNS address set to a local static IP instead of "Auto", so that it receives the DHCP determined DNS IP. Restoring the DHCP DNS setting instantly resolves the issue.
The only thing suspect was WebRoot DNS Filtering, as I could see how it might redirect DNS requests of the client to itself in order to filter. And if it needs to do that, that would be fine except that it ain't working, can't surf and can't send / receive email when WebRoot is handling DNS.