Game Crash on any single player world load/generation

Crash Report: http://pastebin.com/WKsqMeKB
Game Crash on any single player world load/generation

What I expected to happen was...:
Describe what you thought should happen here

What actually happened was...:
The game hanged on Generating Terrain then crashed

Steps to Reproduce:
1. Create or load a new single player world

I really don't know why this is happening and is bugging me.