Internal Exception, Can't join in server

i cant join the server i put mods in. i tried resetting the world but it keeps popping up with this. can someone help?

tried it, still doesnt work

The log doesn't really help either. I'm currently going to try doing troubleshooting it manually to see if what causes this

Okay, so what I found is the mods are not the cause, nor the map. I made a new server and installed the same mods and map and now it's working. Could it be the server's fault?