I just tried to use the tool in Win 10 x64 (fully updated) and was able to host while offline. The tool authenticated the server and allowed it to host. Are you running the tool in admin mode? Try to disable windows firewall? Perhaps an anti-virus program is interfering? Are you keeping the tool open while trying to host a game?
After you launch the tool and the info is written to the hosts file, if you open a command prompt and ping novaworld.net, what does it say?
04' Dodge SRT-4, Mopar Stage 3, 406whp/436wtq