The pacman minecraft world of Dragnoz

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here
I would change gamemode to adventure because i am in an adventure map
What actually happened was...:
Describe what happened here
The screen turned light blue and the Minecraft 1.7.2 gameplay window closed
Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. Enter the world
3. Wait ~10 seconds and it crashes