Pardon if someone else has already answered this but Custom Mob Spawner is NOT a dependency of MoCreatures. I know it says it's required - and it used to be a dependency - but now MoCreatures runs without it. Just as well too because it's poo. If you do need a proper mob spawner, go with JAS. Otherwise, just remove Custom Mob Spawner, edit the MoCreatures config directly and you should be good
Ah okay, thanks for clearing that up.