So I followed this guide step by step: https://www.ahoyworld.net/awe/how-to-join-awe/
I didn't have any problems or hiccups during the process, everything went smoothly.
However, whenever I attempt to join the server, I get this error: (In the image attached)
I assume I am missing a mod or set of mods somewhere, but I am not sure what that mod would be.