snapshot 13w01a single player crash

Simply put, minecraft crashes when I try to open single player with 13w01a installed. I just click on single player on the main menu, it appears to be loading for a few seconds, then crash.

If it helps, here's the crash report from my .minecraft folder;

---- Minecraft Crash Report ----
// Hey, that tickles! Hehehe!

Time: 1/3/13 6:36 PM
Description: Updating screen events

java.lang.SecurityException: SHA1 digest error for aux.class
	at sun.security.util.ManifestEntryVerifier.verify(Unknown Source)
	at java.util.jar.JarVerifier.processEntry(Unknown Source)
	at java.util.jar.JarVerifier.update(Unknown Source)
	at java.util.jar.JarVerifier$VerifierStream.read(Unknown Source)
	at sun.misc.Resource.getBytes(Unknown Source)
	at java.net.URLClassLoader.defineClass(Unknown Source)
	at java.net.URLClassLoader.access$000(Unknown Source)
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at bfm.a(SourceFile:183)
	at auy.a(SourceFile:72)
	at bfm.a(SourceFile:414)
	at auy.d(SourceFile:127)
	at auy.m(SourceFile:111)
	at net.minecraft.client.Minecraft.l(SourceFile:1086)
	at net.minecraft.client.Minecraft.J(SourceFile:582)
	at net.minecraft.client.Minecraft.run(SourceFile:534)
	at java.lang.Thread.run(Unknown Source)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
	at sun.security.util.ManifestEntryVerifier.verify(Unknown Source)
	at java.util.jar.JarVerifier.processEntry(Unknown Source)
	at java.util.jar.JarVerifier.update(Unknown Source)
	at java.util.jar.JarVerifier$VerifierStream.read(Unknown Source)
	at sun.misc.Resource.getBytes(Unknown Source)
	at java.net.URLClassLoader.defineClass(Unknown Source)
	at java.net.URLClassLoader.access$000(Unknown Source)
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at bfm.a(SourceFile:183)
	at auy.a(SourceFile:72)
	at bfm.a(SourceFile:414)
	at auy.d(SourceFile:127)
	at auy.m(SourceFile:111)

-- Affected screen --
Details:
	Screen name: bfm
Stacktrace:
	at net.minecraft.client.Minecraft.l(SourceFile:1086)
	at net.minecraft.client.Minecraft.J(SourceFile:582)
	at net.minecraft.client.Minecraft.run(SourceFile:534)
	at java.lang.Thread.run(Unknown Source)

-- System Details --
Details:
	Minecraft Version: 13w01a
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.6.0_27, Sun Microsystems Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Sun Microsystems Inc.
	Memory: 471707600 bytes (449 MB) / 514523136 bytes (490 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 2 total; -Xms512m -Xmx1024m
	AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	LWJGL: 2.4.2
	OpenGL: Intel(R) HD Graphics Family GL version 3.0.0 - Build 8.15.10.2291, Intel
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Texture Pack: Default
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: ~~ERROR~~ NullPointerException: null