help [Help] Creating my own modpack, encountered a problem running it. looks like a simple fix! Any idea? HELP!!!

[Yucky_Guppy]

I'll be playing with friends on a world then then we convert over to a new modpack that contains all the same mods plus a few new ones, we have good connection but everyone but the host "falls" through the world. Like they have no collision with any blocks and see through the world and can't do anything! 

Edited January 16, 2016 by Yucky_Guppy

[jumpandshootbeef]

I'll be playing with friends on a world then then we convert over to a new modpack that contains all the same mods plus a few new ones, we have good connection but everyone but the host "falls" through the world. Like they have no collision with any blocks and see through the world and can't do anything! 

Thats lagg my friend  . Or if it still keeps happening its a weird bug, then send me the fml-latest.log. does your console say something like: cant keep up, skipping (xxxx) ticks