When I try to join a direct server, I don't know why my minecraft 1.6.1 directly crash

Put the summary of the bug you're having here

What I expected to happen was...
Describe what you thought should happen here
Join the server
What actually happened was...:
Describe what happened here
Minecraft crash
Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
3. ...