@demonsako I downloaded the Manual Mod Install Package, dropped the contents to the root of the "Halo 2 Project Cartographer" install directory and fired up the game. I still get the same error message when trying to join official 0.5.6.0 servers. I also changed my "base_port" to "23453" in my "halo2config1.ini" file as @Big TwEEkx recommended to someone else but no luck.