This just happened to me in 13w10a, the latest snapshot, on march 4th 2013. Crash log below:
Minecraft has crashed!
----------------------
Minecraft has stopped running because it encountered a problem; Adding entity to track
A full error report has been saved to C:\Users\Samson\Desktop\Minecraft\MultiMC 4.1\instances\SSP 1.4.5\minecraft\crash-reports\crash-2013-03-04_21.49.08-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 b932c3bd --------
Full report at:
C:\Users\Samson\Desktop\Minecraft\MultiMC 4.1\instances\SSP 1.4.5\minecraft\crash-reports\crash-2013-03-04_21.49.08-server.txt
Please show that file to Mojang, NOT just this screen!
Generated 3/4/13 9:49 PM
-- Entity To Track --
Details:
Tracking range: 144 blocks
Update interval: Once per 20 ticks
Entity Type: FallingSand (ra)
Entity ID: 17202
Entity Name: Falling Block
Entity's Exact location: -192.50, 27.50, 676.50
Entity's Block location: World: (-193,27,676), Chunk: (at 15,1,4 in -13,42; contains blocks -208,0,672 to -193,255,687), Region: (-1,1; contains chunks -32,32 to -1,63, blocks -512,0,512 to -1,255,1023)
Entity's Momentum: 0.00, 0.00, 0.00
Immitating block ID: 13
Immitating block data: 0
Stacktrace:
at it.a(SourceFile:76)
at it.a(SourceFile:61)
at iv.a(SourceFile:24)
at zv.a(SourceFile:867)
at iz.a(SourceFile:632)
at zv.d(SourceFile:859)
at amn.k(SourceFile:55)
at amn.a(SourceFile:35)
-- Block being ticked --
Details:
Block type: ID #13 (tile.gravel // amk)
Block data value: 0 / 0x0 / 0b0000
Block location: World: (-193,27,676), Chunk: (at 15,1,4 in -13,42; contains blocks -208,0,672 to -193,255,687), Region: (-1,1; contains chunks -32,32 to -1,63, blocks -512,0,512 to -1,255,1023)
Stacktrace:
at iz.a(SourceFile:430)
at iz.b(SourceFile:142)
-- Affected level --
Details:
Level name: New World
All players: 1 total; [jc['Lothrazar'/7726, l='New World', x=-227.50, y=65.00, z=674.50]]
Chunk stats: ServerChunkCache: 733 Drop: 0
Level seed: -6632628904737236560
Level generator: ID 00 - default, ver 1. Features enabled: true
Level generator options:
Level spawn location: World: (-221,64,682), Chunk: (at 3,4,10 in -14,42; contains blocks -224,0,672 to -209,255,687), Region: (-1,1; contains chunks -32,32 to -1,63, blocks -512,0,512 to -1,255,1023)
Level time: 329 game time, 329 day time
Level dimension: 0
Level storage version: 0x04ABD - Anvil
Level weather: Rain time: 43642 (now: false), thunder time: 176002 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: true
Stacktrace:
at net.minecraft.server.MinecraftServer.r(SourceFile:454)
at net.minecraft.server.MinecraftServer.q(SourceFile:397)
at bja.q(SourceFile:122)
at net.minecraft.server.MinecraftServer.run(SourceFile:331)
at gp.run(SourceFile:573)
-- System Details --
Details:
Minecraft Version: 13w10a
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.7.0_13, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 290034168 bytes (276 MB) / 514523136 bytes (490 MB) up to 1140850688 bytes (1088 MB)
JVM Flags: 2 total; -Xms512m -Xmx1224m
AABB Pool Size: 7769 (435064 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 63
Profiler Position: N/A (disabled)
Vec3 Pool Size: 5963 (333928 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Player Count: 1 / 8; [jc['Lothrazar'/7726, l='New World', x=-227.50, y=65.00, z=674.50]]
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 it.a(SourceFile:76)
at it.a(SourceFile:61)
at iv.a(SourceFile:24)
at zv.a(SourceFile:867)
at iz.a(SourceFile:632)
at zv.d(SourceFile:859)
at amn.k(SourceFile:55)
at amn.a(SourceFile:35)
at iz.a(SourceFile:430)
at iz.b(SourceFile:142)
at net.minecraft.server.MinecraftServer.r(SourceFile:454)
at net.minecraft.server.MinecraftServer.q(SourceFile:397)
at bja.q(SourceFile:122)
at net.minecraft.server.MinecraftServer.run(SourceFile:331)
at gp.run(SourceFile:573)
--- END ERROR REPORT 7e052989 ----------
Just to add more information to the comment above, this didnt just happen in the snapshot, but it was a new world created in the 13w10a snapshot. (however, snapshot may not matter as this report looks to be originally from 1.4.2).
I created a new creative world to test some things, right away I opened my inventory and added some items to my hotbar (minecart and something else), then this happened.
After the crash, i can reload the game, load the same world, and the crash does not happen again. I have to assume this only happens when generating new chunks, and then a falling block (in my case gravel) gets tracked twice.