[PC - GRFS] A solution for some of those unable to connect to games
If you are unable to connect to games (get told No Sessions Are Found or that you are unable to connect to a host in a coop game,) and have already tried forwarding ports and all of the other typical things with firewalls and antivirus software with no luck, the answer may be in Hamachi.
If you have Hamachi installed (or Tuungle, or anything similar,) DISABLE the network adapter that it installs. You can do this through both the Device Manager and the adapter settings in the Network section of the Control Panel. Make sure ALL network adapters except for the one you use to access the internet are disabled just to be safe and then try again.
The explanation for this behavior is in the priority that network adapters are used by some software. In some installations, the Hamachi (or Tuungle, etc) network adapter is the one that GRFW is using. Since this adapter only connects you to the Hamachi network you're a part of, you are unable to access the internet and thus the game. Not all software does this, but GRFW does.