crashes when you try and access your inventory/chest/crafting table/furnace etc

Minecraft Crash Report ----
// I blame Dinnerbone.

Time: 04/07/13 16:58
Description: Unexpected error

java.lang.NoClassDefFoundError: _tmi_MgButtonHandler
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClassCond(Unknown Source)
	at java.lang.ClassLoader.defineClass(Unknown Source)
	at java.security.SecureClassLoader.defineClass(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 TMI.<init>(TMI.java:7)
	at TMI.<clinit>(TMI.java:6)
	at ayl.<init>(ayl.java:45)
	at azb.<init>(SourceFile:16)
	at azg.<init>(SourceFile:19)
	at net.minecraft.client.Minecraft.l(SourceFile:1266)
	at net.minecraft.client.Minecraft.K(SourceFile:574)
	at net.minecraft.client.Minecraft.run(SourceFile:526)
	at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: _tmi_MgButtonHandler
	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)
	... 20 more


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

-- Head --
Stacktrace:
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClassCond(Unknown Source)
	at java.lang.ClassLoader.defineClass(Unknown Source)
	at java.security.SecureClassLoader.defineClass(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 TMI.<init>(TMI.java:7)
	at TMI.<clinit>(TMI.java:6)
	at ayl.<init>(ayl.java:45)
	at azb.<init>(SourceFile:16)
	at azg.<init>(SourceFile:19)

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bdv['SJHPhoenix'/8935251, l='MpServer', x=176.95, y=65.12, z=34.75]]
	Chunk stats: MultiplayerChunkCache: 121
	Level seed: 0
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn location: World: (193,63,100), Chunk: (at 1,3,4 in 12,6; contains blocks 192,0,96 to 207,255,111), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Level time: 312041584 game time, 317957590 day time
	Level dimension: 0
	Level storage version: 0x00000 - Unknown?
	Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
	Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
	Forced entities: 20 total; [ru['Creeper'/8934142, l='MpServer', x=215.50, y=13.00, z=0.50], bdv['SJHPhoenix'/8935251, l='MpServer', x=176.95, y=65.12, z=34.75], ru['Creeper'/8933564, l='MpServer', x=177.03, y=59.00, z=63.41], sj['Zombie'/8933857, l='MpServer', x=215.50, y=49.00, z=68.31], ru['Creeper'/8933559, l='MpServer', x=208.00, y=17.00, z=53.50], sh['Spider'/8934928, l='MpServer', x=211.50, y=17.00, z=60.50], ru['Creeper'/8934064, l='MpServer', x=219.47, y=51.00, z=3.16], ru['Creeper'/8933799, l='MpServer', x=173.50, y=5.00, z=60.97], sf['Skeleton'/8935134, l='MpServer', x=222.50, y=25.00, z=64.09], qo['Sheep'/8934069, l='MpServer', x=137.47, y=69.00, z=9.47], sj['Zombie'/8934059, l='MpServer', x=175.50, y=15.00, z=13.78], ru['Creeper'/8933549, l='MpServer', x=216.50, y=50.00, z=65.50], sf['Skeleton'/8933548, l='MpServer', x=190.50, y=46.00, z=73.91], sj['Zombie'/8934063, l='MpServer', x=212.50, y=31.00, z=0.50], sj['Zombie'/8934062, l='MpServer', x=210.88, y=13.00, z=1.44], sh['Spider'/8934926, l='MpServer', x=213.72, y=17.00, z=53.50], rn['entity.MinecartRideable.name'/8934060, l='MpServer', x=175.47, y=59.34, z=1.50], sf['Skeleton'/8934499, l='MpServer', x=178.50, y=12.00, z=-1.50], sj['Zombie'/8934054, l='MpServer', x=216.50, y=17.00, z=49.50], sj['Zombie'/8934053, l='MpServer', x=217.50, y=17.00, z=48.50]]
	Retry entities: 0 total; []
Stacktrace:
	at bds.a(SourceFile:282)
	at net.minecraft.client.Minecraft.b(SourceFile:1881)
	at net.minecraft.client.Minecraft.run(SourceFile:540)
	at java.lang.Thread.run(Unknown Source)

-- System Details --
Details:
	Minecraft Version: 1.5.2
	Operating System: Windows Vista (x86) version 6.0
	Java Version: 1.6.0_22, Sun Microsystems Inc.
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Sun Microsystems Inc.
	Memory: 420341032 bytes (400 MB) / 519110656 bytes (495 MB) up to 1037959168 bytes (989 MB)
	JVM Flags: 2 total; -Xms512m -Xmx1024m
	AABB Pool Size: 15932 (892192 bytes; 0 MB) allocated, 2 (112 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 63
	LWJGL: 2.4.2
	OpenGL: GeForce 9300 GE/PCI/SSE2/3DNOW! GL version 2.1.2, NVIDIA Corporation
	Is Modded: Very likely; Jar signature invalidated
	Type: Client (map_client.txt)
	Texture Pack: Default
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 3371 (188776 bytes; 0 MB) allocated, 17 (952 bytes; 0 MB) used