I loaded up the world and it crashed!

---- Minecraft Crash Report ----
// I just don't know what went wrong :(

Time: 31/05/13 12:15
Description: Loading entity NBT

java.lang.UnsupportedOperationException: Cannot modify readonly attribute
	at oi.a(SourceFile:54)
	at sx.a(SourceFile:87)
	at sx.a(SourceFile:70)
	at np.a(SourceFile:348)
	at nq.a(SourceFile:251)
	at mx.f(SourceFile:1061)
	at aas.a(SourceFile:116)
	at aas.h(SourceFile:234)
	at bhk.a(SourceFile:22)
	at bhk.a(SourceFile:17)
	at bhk.a(SourceFile:12)
	at bhp.a(SourceFile:106)
	at bhp.a(SourceFile:98)
	at bdz.a(SourceFile:317)
	at bds.a(SourceFile:836)
	at bds.b(SourceFile:682)
	at asx.R(SourceFile:674)
	at asx.d(SourceFile:607)
	at net.minecraft.client.main.Main.main(SourceFile:78)


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

-- Head --
Stacktrace:
	at oi.a(SourceFile:54)
	at sx.a(SourceFile:87)
	at sx.a(SourceFile:70)
	at np.a(SourceFile:348)
	at nq.a(SourceFile:251)

-- Entity being loaded --
Details:
	Entity Type: Blaze (sl)
	Entity ID: 2726
	Entity Name: Blaze
	Entity's Exact location: 0.00, 0.00, 0.00
	Entity's Block location: World: (0,0,0), Chunk: (at 0,0,0 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Entity's Momentum: 0.00, -0.08, 0.00
Stacktrace:
	at mx.f(SourceFile:1061)
	at aas.a(SourceFile:116)
	at aas.h(SourceFile:234)
	at bhk.a(SourceFile:22)
	at bhk.a(SourceFile:17)
	at bhk.a(SourceFile:12)

-- Tile Entity Details --
Details:
	Name: MobSpawner // arm
	Block type: ID #52 (tile.mobSpawner // aol)
	Block data value: 0 / 0x0 / 0b0000
	Block location: World: (-853,73,-605), Chunk: (at 11,4,3 in -54,-38; contains blocks -864,0,-608 to -849,255,-593), Region: (-2,-2; contains chunks -64,-64 to -33,-33, blocks -1024,0,-1024 to -513,255,-513)
	Actual block type: ID #52 (tile.mobSpawner // aol)
	Actual block data value: 0 / 0x0 / 0b0000
Stacktrace:
	at bhp.a(SourceFile:106)
	at bhp.a(SourceFile:98)
	at bdz.a(SourceFile:317)
	at bds.a(SourceFile:836)

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bbw['dom_g_t'/25, l='MpServer', x=-854.49, y=58.62, z=-598.76]]
	Chunk stats: MultiplayerChunkCache: 145
	Level seed: 0
	Level generator: ID 01 - flat, ver 0. Features enabled: false
	Level generator options: 
	Level spawn location: World: (-823,4,-674), Chunk: (at 9,0,14 in -52,-43; contains blocks -832,0,-688 to -817,255,-673), Region: (-2,-2; contains chunks -64,-64 to -33,-33, blocks -1024,0,-1024 to -513,255,-513)
	Level time: 69611 game time, 5002 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: creative (ID 1). Hardcore: false. Cheats: false
	Forced entities: 15 total; [qy['Chicken'/8, l='MpServer', x=-896.47, y=57.00, z=-642.44], bbw['dom_g_t'/25, l='MpServer', x=-854.49, y=58.62, z=-598.76], rg['Pig'/9, l='MpServer', x=-896.09, y=57.00, z=-630.03], rg['Pig'/10, l='MpServer', x=-901.31, y=57.00, z=-621.91], rg['Pig'/11, l='MpServer', x=-899.23, y=57.00, z=-622.64], rg['Pig'/12, l='MpServer', x=-909.78, y=57.00, z=-622.69], qy['Chicken'/13, l='MpServer', x=-892.53, y=57.00, z=-624.53], qy['Chicken'/14, l='MpServer', x=-893.38, y=57.00, z=-628.69], sa['item.item.egg'/15, l='MpServer', x=-893.78, y=57.13, z=-631.06], qy['Chicken'/17, l='MpServer', x=-885.47, y=57.00, z=-634.56], sa['item.item.egg'/16, l='MpServer', x=-892.66, y=57.13, z=-626.88], tg['Villager'/18, l='MpServer', x=-875.25, y=57.00, z=-626.04], ra['Horse'/20, l='MpServer', x=-855.50, y=57.00, z=-635.81], ra['Mule'/23, l='MpServer', x=-816.53, y=57.00, z=-669.78], ra['Horse'/22, l='MpServer', x=-827.34, y=57.00, z=-673.00]]
	Retry entities: 0 total; []
Stacktrace:
	at bbt.a(SourceFile:282)
	at asx.b(SourceFile:1793)
	at asx.d(SourceFile:616)
	at net.minecraft.client.main.Main.main(SourceFile:78)

-- System Details --
Details:
	Minecraft Version: 13w22a
	Operating System: Windows 8 (amd64) version 6.2
	Java Version: 1.7.0_13, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 236126144 bytes (225 MB) / 531234816 bytes (506 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 21812 (1221472 bytes; 1 MB) allocated, 690 (38640 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	LWJGL: 2.9.0
	OpenGL: AMD Radeon HD 6550D GL version 4.2.12002 Compatibility Profile Context 9.12.0.0, ATI Technologies Inc.
	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: 145 (8120 bytes; 0 MB) allocated, 145 (8120 bytes; 0 MB) used