Minecraft Crashes when logging in.

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: ~_ERROR~ NullPointerException: null
Is Modded: Very likely; Jar signature invalidated

Minecraft Crash Report ----
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Time: 2/23/13 12:04 PM
Description: Unexpected error

java.lang.NullPointerException
at org.lwjgl.opengl.GL11.glGetError(GL11.java:1279)
at net.minecraft.client.Minecraft.d(SourceFile:464)
at net.minecraft.client.Minecraft.J(SourceFile:586)
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:
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: ~_ERROR~ NullPointerException: null
Is Modded: Very likely; Jar signature invalidated
Type: Client (map_client.txt)
Texture Pack: Default
Profiler Position: N/A (disabled)
Vec3 Pool Size: ~_ERROR~ NullPointerException: null