minecraft crash when open map

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

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

A full error report has been saved to C:\Documents and Settings\admin\Application Data\.minecraft\crash-reports\crash-2012-12-03_17.56.02-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 f75f9e8d --------
Full report at:
C:\Documents and Settings\admin\Application Data\.minecraft\crash-reports\crash-2012-12-03_17.56.02-server.txt
Please show that file to Mojang, NOT just this screen!

Generated 2012/12/3 下午 5:56

-- Head --
Stacktrace:
        at ii.a(SourceFile:72)
        at ii.a(SourceFile:50)
        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 px.b(SourceFile:201)
        at amg.a(SourceFile:62)
        at lq.D(SourceFile:652)
        at lq.d(SourceFile:615)
        at px.j_(SourceFile:67)
        at xv.a(SourceFile:1317)
        at in.a(SourceFile:451)
        at xv.g(SourceFile:1296)

-- Entity being ticked --
Details:
        Entity Type: Item (px)
        Entity ID: 162
        Name: item.item.minecart
        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: 0.02, -0.25, 0.04
Stacktrace:
        at xv.h(SourceFile:1195)
        at in.h(SourceFile:363)

-- Affected level --
Details:
        Level name: 成就地圖(自製) BY WILLIAM
        All players: 1 total; [iq['Sunny1121'/157, l='成就地圖(自製) BY WILLIAM', x=94.70, y=55.15, z=6.50]]
        Chunk stats: ServerChunkCache: 441 Drop: 0
        Level seed: 5684308328351284188
        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: Windows XP (x86) version 5.1
        Java Version: 1.7.0_09, Oracle Corporation
        Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
        Memory: 465724744 bytes (444 MB) / 658898944 bytes (628 MB) up to 658898944 bytes (628 MB)
        JVM Flags: 1 total; -Xms650m
        AABB Pool Size: 3095 (173320 bytes; 0 MB) allocated, 1633 (91448 bytes; 0 MB) used
        Suspicious classes: No suspicious classes found.
        IntCache: cache: 0, tcache: 0, allocated: 1, tallocated: 71
        Profiler Position: N/A (disabled)
        Vec3 Pool Size: 208 (11648 bytes; 0 MB) allocated, 198 (11088 bytes; 0 MB) used
        Player Count: 1 / 8; [iq['Sunny1121'/157, l='成就地圖(自製) BY WILLIAM', x=94.70, y=55.15, z=6.50]]
        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:50)
        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 px.b(SourceFile:201)
        at amg.a(SourceFile:62)
        at lq.D(SourceFile:652)
        at lq.d(SourceFile:615)
        at px.j_(SourceFile:67)
        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 9a20f20c ----------