Game crashes when entering end portal

I was playing on my hardcore mode game, i wanted to go back to the end to get the egg. After i jumped into the portal, the game froze and it gave me this message. I have been playing this hardcore mode game for months now, please help me solve the problem.

Minecraft has crashed!      
      ----------------------      

Minecraft has stopped running because it encountered a problem; Ticking entity

A full error report has been saved to /Users/linea2/Library/Application Support/minecraft/crash-reports/crash-2012-12-11_18.42.12-server.txt - Please include a copy of that file (Not this screen!) if you report this crash to anyone; without it, they will not be able to help fix the crash :(



--- BEGIN ERROR REPORT 203159b1 --------
Full report at:
/Users/linea2/Library/Application Support/minecraft/crash-reports/crash-2012-12-11_18.42.12-server.txt
Please show that file to Mojang, NOT just this screen!

Generated 11/12/12 18:42

-- Head --
Stacktrace:
	at ii.a(SourceFile:72)
	at ii.a(SourceFile:61)
	at ij.a(SourceFile:24)
	at xv.a(SourceFile:842)
	at in.a(SourceFile:581)
	at xv.d(SourceFile:834)
	at gm.a(SourceFile:369)
	at lq.b(SourceFile:1492)
	at amg.a(SourceFile:62)
	at lq.D(SourceFile:652)
	at lq.d(SourceFile:615)
	at lz.j_(SourceFile:111)
	at xv.a(SourceFile:1317)
	at in.a(SourceFile:451)
	at xv.g(SourceFile:1296)

-- Entity being ticked --
Details:
	Entity Type: XPOrb (lz)
	Entity ID: 191
	Name: Experience Orb
	Exact location: 100,00, 50,13, 0,00
	Block location: World: (100,50,0), Chunk: (at 4,3,0 in 6,0; contains blocks 96,0,0 to 111,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Momentum: -0,03, 0,17, -0,00
Stacktrace:
	at xv.h(SourceFile:1195)
	at in.h(SourceFile:363)

-- Affected level --
Details:
	Level name: Peteyland
	All players: 1 total; [iq['peteysanz'/152, l='Peteyland', x=100,00, y=49,00, z=0,00]]
	Chunk stats: ServerChunkCache: 441 Drop: 0
	Level seed: -273318909269376691
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn 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)
	Level time: 0 game time, 0 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: ~~ERROR~~ NullPointerException: null
Stacktrace:
	at net.minecraft.server.MinecraftServer.r(SourceFile:751)
	at net.minecraft.server.MinecraftServer.q(SourceFile:686)
	at bdo.q(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:620)
	at fy.run(SourceFile:856)

-- System Details --
Details:
	Minecraft Version: 1.4.5
	Operating System: Mac OS X (x86_64) version 10.5.8
	Java Version: 1.6.0_26, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 465496040 bytes (443 MB) / 554369024 bytes (528 MB) up to 1069416448 bytes (1019 MB)
	JVM Flags: 3 total; -Xbootclasspath/a:/System/Library/PrivateFrameworks/JavaApplicationLauncher.framework/Resources/LauncherSupport.jar -Xms512M -Xmx1024M
	AABB Pool Size: 2284 (127904 bytes; 0 MB) allocated, 2256 (126336 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 1, tallocated: 63
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 314 (17584 bytes; 0 MB) allocated, 301 (16856 bytes; 0 MB) used
	Player Count: 1 / 8; [iq['peteysanz'/152, l='Peteyland', x=100,00, y=49,00, z=0,00]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.

java.lang.IllegalStateException: Entity is already tracked!
	at ii.a(SourceFile:72)
	at ii.a(SourceFile:61)
	at ij.a(SourceFile:24)
	at xv.a(SourceFile:842)
	at in.a(SourceFile:581)
	at xv.d(SourceFile:834)
	at gm.a(SourceFile:369)
	at lq.b(SourceFile:1492)
	at amg.a(SourceFile:62)
	at lq.D(SourceFile:652)
	at lq.d(SourceFile:615)
	at lz.j_(SourceFile:111)
	at xv.a(SourceFile:1317)
	at in.a(SourceFile:451)
	at xv.g(SourceFile:1296)
	at xv.h(SourceFile:1195)
	at in.h(SourceFile:363)
	at net.minecraft.server.MinecraftServer.r(SourceFile:751)
	at net.minecraft.server.MinecraftServer.q(SourceFile:686)
	at bdo.q(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:620)
	at fy.run(SourceFile:856)
--- END ERROR REPORT 33168778 ----------