When Brain Slime jumps on me in my game: items don't drop, mobs don't move or attack, sand don't fall. i can only move and build and break.When im exiting to menu minecraft crashes.I think I will have to delete this mod.

Im not playing on server. Im using newest 1.2.3a. I use more than 100 other mods

How to epair this or disable brain slime spawning?

This bug is very rare and hard to track so far. I recommend looking into the primitivemobs.cfg config file and setting brain slimes to false.