Multiplayer: Can't connect to server

When I go to access my multiplayer server, it cannot connect to the server. The host server has been updated to the same version. Host computer can connect to the server that it runs on. Both users on other systems can no longer locate the server. Did not have this issue with 1.6.4, which was our last update before this version.

Update: Issue resolved by disabling firewall and reinstalling Hamachi!