To Reproduce
Steps to reproduce the crash:

1. Log in to my modded server
2. Play for a little while, do nothing in particular
3. Randomly Minecraft crashes, happens when mining / farming, whatever. Seems to be unrelated to what I do
4. Everytime I log into the server, I instantly crash

Screenshots

Versions (please complete the following information)

• Forge: 1.7.10-Forge10.13.4.1558-1.7.10
• Flan's Mod: Flans Mod-1.7.10-4.10.0

Crash Log
https://gist.github.com/HenkDeKipGaming/11aa3fd9048369097a15946e291c9de8

Additional context
I'm using flan packs:

• British Military Pack V1.131
• Modern Warfare-Content Pack-1.7.10-4.10.0
• Simple Parts-Content Pack-1.7.10-4.10.0
• WW2-Content Pack-1.7.10-4.10.0

The modpack works perfectly until I add flans mod. It doesn't only happen to me, my friends also crash.
The weird thing is that the client also crashes if it has flansmod installed while the server does not. Deleting flansmod from the mods folder solved everything.

Also, the server gives this error when I join en crash: https://gist.github.com/HenkDeKipGaming/c8341e7c46e632cb5e1503b04ed51dc2

We are sorry, but Flans Mod for 1.7.10 is no longer supported

:( This makes me sad, Minecraft 1.7.10 was the absolute best version for mods and modpacks. I loved using it until this bug.
It makes no sense though, everything worked fine for a whole week and than suddenly everything stopped working