Would you post your full crash log? There is likely a mod that manipulates entities (specifically Ender Man). Since Ender Man are hostile mobs and they don't spawn in peaceful mode , check any mods that manipulate Ender Man, mob spawning, enemy AI, and the like.
Alternatively, you can load single mods at a time and find out which is causing the crash.
Something wasn't allocated properly, but with little knowledge of mods, and it appearing as a standard mob spawn, I'm not exactly sure where to start. Gut says its something related to one of your mob-related mods, but I have nothing to go on other than you have a ton of them (: