Forge Mod Loader is a mod that isnt allowed to be used on the server apparently. Even though FML doesnt add anything more to the game. I was just wondering why because FML is a major mod compatibility mod. I just keep failing to join. Thanks for your time!
The message is saying that you do not have the correct TerraFirmaCraft version installed. Please install the latest version (0.79.18) from the TerraFirmaCraft website.