NW Authenticator allows you to host LW/TFD/BHD/C4 even when NovaWorld is down. If you get an "Unable to host a Session" message when trying to host a game, most likely NovaWorld is down and another method to authenticate your game will be required. Open this tool before loading your game and it will attempt to locally authenticate your games session. If you get an "Unable to Host a Session" message when hosting, this is what you need.
Your game will still appear on NovaWorld. Please ask for help in the forums if it does not work for you.