game crashes as soon as downloading terrain finishes

Put the summary of the bug you're having here

What I expected to happen was...:
To be able to walk after the world loaded.
What actually happened was...:
As soon as I saw the world, the game crashed and an error log popped up.

Steps to Reproduce:
1. open launcher and launch with my profile on 14w30c
2. log onto friend's server
3. game crashes when world comes into focus