Minecraft Forums

I made this temporary fix for this crash until next patch comes out. https://www.box.com/s/a7kntgysrdo3ri6z6bve.
Here is the source. https://www.box.com/s/5ovv62t6xeilj25a1y3z.
You can compile yourself using MCP http://www.mediafire.com/?rz8dnqj1bxrz85q by placing the java file into \src\minecraft\net\minecraft\src\, recompiling, and reobfuscating. The output will be in \reobf\minecraft\.

Installation:
1. Close Minecraft.
2. Using 7-zip or w/e; Open minecraft.jar located in Users/Name/AppData/Roaming/.minecraft/bin/ for windows 7.
3. Remove directory META-INF/ in minecraft.jar file.
4. Place the downloaded lt.class in minecraft.jar file.

Quote from Syfaro

Could you please diff the original and the new file? I'm interested in seeing exactly what you changed.

Pretty much just added instanceof check within getWatchableObjectByte() declaration. It however does not fix the origin of the problem.