NaviLlicious

I'm not sure this is the right place if it's not sorry D:, I have been looking around for a solution to my problem but can't find one. I installed Mo Creatures to my 1.7.2 cauldron server but noticed barely any mobs spawn, I just played on the server with some friends for a couple hours and barely saw any hostile mobs, I also noticed that in the console it said "Skipping entity with id Skeleton" or "Skipping entity with id Zombie". I'm not sure if that's related or not, does anyone know how to fix this?