Game randomly crashing

I randomly crash when in a certain world. It doesn't happen in any other worlds, or in any other versions. It happened when I went near a mob spawner. It doesn't happen when spawners of this mob are not activated.

The log:

---- Minecraft Crash Report ----
// Oh - I know what I did wrong!

Time: 23/05/13 20:39
Description: Loading entity NBT

java.lang.NullPointerException
	at np.a(SourceFile:357)
	at nq.a(SourceFile:251)
	at sz.a(SourceFile:297)
	at mx.f(SourceFile:1061)
	at aas.a(SourceFile:116)
	at aas.h(SourceFile:234)
	at bhe.a(SourceFile:22)
	at bhe.a(SourceFile:17)
	at bhe.a(SourceFile:12)
	at bhj.a(SourceFile:106)
	at bhj.a(SourceFile:98)
	at bdt.a(SourceFile:317)
	at bdm.a(SourceFile:836)
	at bdm.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 np.a(SourceFile:357)
	at nq.a(SourceFile:251)
	at sz.a(SourceFile:297)

-- Entity being loaded --
Details:
	Entity Type: Skeleton (sz)
	Entity ID: 34341
	Entity Name: Skeleton
	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, 0.00, 0.00
Stacktrace:
	at mx.f(SourceFile:1061)
	at aas.a(SourceFile:116)
	at aas.h(SourceFile:234)
	at bhe.a(SourceFile:22)
	at bhe.a(SourceFile:17)
	at bhe.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: (688,148,1342), Chunk: (at 0,9,14 in 43,83; contains blocks 688,0,1328 to 703,255,1343), Region: (1,2; contains chunks 32,64 to 63,95, blocks 512,0,1024 to 1023,255,1535)
	Actual block type: ID #52 (tile.mobSpawner // aol)
	Actual block data value: 0 / 0x0 / 0b0000
Stacktrace:
	at bhj.a(SourceFile:106)
	at bhj.a(SourceFile:98)
	at bdt.a(SourceFile:317)
	at bdm.a(SourceFile:836)

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bbq['MinerMinerMiney'/13, l='MpServer', x=677.00, y=168.86, z=1401.87]]
	Chunk stats: MultiplayerChunkCache: 441
	Level seed: 0
	Level generator: ID 01 - flat, ver 0. Features enabled: false
	Level generator options: 
	Level spawn location: World: (629,169,1397), Chunk: (at 5,10,5 in 39,87; contains blocks 624,0,1392 to 639,255,1407), Region: (1,2; contains chunks 32,64 to 63,95, blocks 512,0,1024 to 1023,255,1535)
	Level time: 3104416 game time, 1073704 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: 12 total; [nn['entity.ItemFrame.name'/1, l='MpServer', x=613.50, y=122.50, z=1504.94], nn['entity.ItemFrame.name'/2, l='MpServer', x=611.50, y=122.50, z=1504.94], qz['Cow'/4, l='MpServer', x=654.56, y=157.00, z=1431.38], rg['Pig'/5, l='MpServer', x=677.50, y=144.00, z=1336.50], rj['Snow Golem'/6, l='MpServer', x=685.50, y=146.00, z=1341.50], qy['Chicken'/7, l='MpServer', x=687.47, y=151.00, z=1455.47], qy['Chicken'/8, l='MpServer', x=688.53, y=150.00, z=1455.44], qy['Chicken'/9, l='MpServer', x=688.56, y=149.00, z=1453.63], sa['item.item.egg'/10, l='MpServer', x=688.44, y=149.13, z=1453.50], no['entity.LeashKnot.name'/11, l='MpServer', x=632.50, y=130.50, z=1501.50], no['entity.LeashKnot.name'/12, l='MpServer', x=688.50, y=150.50, z=1456.50], bbq['MinerMinerMiney'/13, l='MpServer', x=677.00, y=168.86, z=1401.87]]
	Retry entities: 0 total; []
Stacktrace:
	at bbn.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: 13w21a
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_11, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
	Memory: 216742368 bytes (206 MB) / 589672448 bytes (562 MB) up to 1037959168 bytes (989 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 5827 (326312 bytes; 0 MB) allocated, 96 (5376 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	LWJGL: 2.9.0
	OpenGL: GeForce 9300M GS/PCI/SSE2 GL version 3.0.0, NVIDIA Corporation
	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: 270 (15120 bytes; 0 MB) allocated, 59 (3304 bytes; 0 MB) used