Blood, we need a Forge Update to fix a server Issue.
I'm currently running Forge 10.13.3.1408, and everything runs fine. The problem is, there are mods in my pack now that are requiring 10.13.3.1448 of Forge or Higher
But when I try to update the recommended forge version of 10.13.3.1448, everything (including Gregtech) boots fine in Single Player Mode. My server also boots fine (on its own).
But, when I try to connect to the server from my client, using 10.13.3.1448, I get the following crash on my client side - but it doesn't crash the server.
I've narrowed it down to Gregtech. If I take out Gregtech, everything connects and works perfectly. As soon as I put it back in on the client and server, it crashes when trying to connect.
I had the exact same problem, but downgrading to Forge 1420 fixed the issue for me.