Hopper: java.util.ConcurrentModificationException

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
	at java.util.HashMap$EntryIterator.next(HashMap.java:834)
	at java.util.HashMap$EntryIterator.next(HashMap.java:832)
	at java.util.HashMap.putAllForCreate(HashMap.java:435)
	at java.util.HashMap.<init>(HashMap.java:225)
	at bls.b(SourceFile:52)
	at bls.e(SourceFile:209)

---- Minecraft Crash Report ----
// You should try our sister game, Minceraft!

Time: 8/2/13 8:52 PM
Description: Unexpected error

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
	at java.util.HashMap$EntryIterator.next(HashMap.java:834)
	at java.util.HashMap$EntryIterator.next(HashMap.java:832)
	at java.util.HashMap.putAllForCreate(HashMap.java:435)
	at java.util.HashMap.<init>(HashMap.java:225)
	at bls.b(SourceFile:52)
	at bls.e(SourceFile:209)
	at ats.k(SourceFile:1129)
	at ats.S(SourceFile:663)
	at ats.d(SourceFile:619)
	at net.minecraft.client.main.Main.main(SourceFile:101)


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

-- Head --
Stacktrace:
	at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
	at java.util.HashMap$EntryIterator.next(HashMap.java:834)
	at java.util.HashMap$EntryIterator.next(HashMap.java:832)
	at java.util.HashMap.putAllForCreate(HashMap.java:435)
	at java.util.HashMap.<init>(HashMap.java:225)
	at bls.b(SourceFile:52)
	at bls.e(SourceFile:209)

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bdf['annepieter'/529566, l='MpServer', x=-104.72, y=12.62, z=132.17]]
	Chunk stats: MultiplayerChunkCache: 441
	Level seed: 0
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn location: World: (-140,64,252), Chunk: (at 4,4,12 in -9,15; contains blocks -144,0,240 to -129,255,255), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
	Level time: 97524 game time, 97524 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: survival (ID 0). Hardcore: false. Cheats: false
	Forced entities: 87 total; [sr['item.item.egg'/793895, l='MpServer', x=-162.56, y=97.13, z=130.75], ts['Spider'/662073, l='MpServer', x=-94.28, y=21.00, z=116.28], tq['Skeleton'/846763, l='MpServer', x=-131.50, y=23.00, z=101.50], tq['Skeleton'/846760, l='MpServer', x=-132.50, y=23.00, z=103.50], tq['Skeleton'/846761, l='MpServer', x=-130.50, y=23.00, z=105.50], tq['Skeleton'/813998, l='MpServer', x=-80.50, y=17.00, z=196.50], tv['Zombie'/813996, l='MpServer', x=-79.00, y=17.00, z=200.63], te['Creeper'/823796, l='MpServer', x=-56.03, y=13.00, z=119.59], tq['Skeleton'/829445, l='MpServer', x=-182.50, y=30.00, z=92.50], rw['Ocelot'/846776, l='MpServer', x=-73.97, y=68.00, z=66.97], rw['Ocelot'/846775, l='MpServer', x=-74.47, y=68.00, z=66.53], te['Creeper'/845667, l='MpServer', x=-120.00, y=16.00, z=108.47], rw['Ocelot'/846774, l='MpServer', x=-77.88, y=69.00, z=64.72], tv['Zombie'/845666, l='MpServer', x=-80.56, y=22.00, z=119.41], rw['Ocelot'/846773, l='MpServer', x=-80.44, y=68.00, z=67.88], te['Creeper'/855558, l='MpServer', x=-85.50, y=23.00, z=122.50], te['Creeper'/855559, l='MpServer', x=-80.50, y=23.00, z=115.50], tv['Zombie'/845649, l='MpServer', x=-100.50, y=25.00, z=148.50], sb['Squid'/834645, l='MpServer', x=-90.50, y=57.34, z=135.50], rn['Bat'/813493, l='MpServer', x=-130.49, y=41.54, z=99.28], tr['Slime'/821354, l='MpServer', x=-63.31, y=52.05, z=154.69], tv['Zombie'/824052, l='MpServer', x=-105.50, y=19.00, z=84.50], tv['Zombie'/838576, l='MpServer', x=-35.50, y=40.00, z=181.50], bdf['annepieter'/529566, l='MpServer', x=-104.72, y=12.62, z=132.17], sr['item.item.egg'/829058, l='MpServer', x=-158.41, y=69.13, z=85.53], sr['item.item.egg'/796081, l='MpServer', x=-170.13, y=93.13, z=113.13], rn['Bat'/811853, l='MpServer', x=-44.28, y=38.10, z=142.25], rp['Chicken'/529510, l='MpServer', x=-167.44, y=78.00, z=146.56], rp['Chicken'/529511, l='MpServer', x=-159.59, y=72.00, z=72.53], rp['Chicken'/529504, l='MpServer', x=-161.50, y=95.00, z=129.50], rw['Ocelot'/836056, l='MpServer', x=-89.50, y=64.00, z=53.50], rp['Chicken'/529505, l='MpServer', x=-164.31, y=93.00, z=137.53], rw['Ocelot'/822244, l='MpServer', x=-101.16, y=72.00, z=60.28], ts['Spider'/820498, l='MpServer', x=-122.22, y=42.00, z=59.34], tq['Skeleton'/836049, l='MpServer', x=-59.50, y=18.00, z=143.50], rp['Chicken'/529512, l='MpServer', x=-152.50, y=75.00, z=86.50], tq['Skeleton'/836048, l='MpServer', x=-59.50, y=18.00, z=141.50], rp['Chicken'/529513, l='MpServer', x=-154.50, y=68.00, z=82.50], tv['Zombie'/854774, l='MpServer', x=-60.50, y=50.00, z=141.94], tv['Zombie'/854772, l='MpServer', x=-58.94, y=49.00, z=142.47], tv['Zombie'/854773, l='MpServer', x=-59.16, y=49.00, z=144.69], rn['Bat'/833975, l='MpServer', x=-89.73, y=31.61, z=123.29], te['Creeper'/839204, l='MpServer', x=-100.50, y=19.00, z=205.50], st['entity.MinecartChest.name'/529532, l='MpServer', x=-78.50, y=17.34, z=201.69], tq['Skeleton'/853041, l='MpServer', x=-37.50, y=23.00, z=149.50], te['Creeper'/835325, l='MpServer', x=-77.00, y=39.00, z=101.56], rp['Chicken'/529495, l='MpServer', x=-181.50, y=69.00, z=190.50], rp['Chicken'/529494, l='MpServer', x=-179.50, y=69.00, z=190.50], tq['Skeleton'/836791, l='MpServer', x=-51.94, y=29.00, z=67.47], rp['Chicken'/529501, l='MpServer', x=-164.31, y=79.00, z=97.47], rp['Chicken'/529502, l='MpServer', x=-171.44, y=93.00, z=113.44], te['Creeper'/853035, l='MpServer', x=-163.50, y=33.00, z=85.50], rp['Chicken'/529496, l='MpServer', x=-179.50, y=69.00, z=190.50], rp['Chicken'/529499, l='MpServer', x=-168.50, y=81.00, z=72.50], te['Creeper'/842870, l='MpServer', x=-182.50, y=20.00, z=78.50], ts['Spider'/835227, l='MpServer', x=-83.11, y=22.95, z=121.30], tq['Skeleton'/843104, l='MpServer', x=-67.50, y=18.00, z=193.50], rn['Bat'/845895, l='MpServer', x=-61.44, y=29.57, z=59.52], sr['item.item.egg'/801964, l='MpServer', x=-149.13, y=78.13, z=87.59], tv['Zombie'/849077, l='MpServer', x=-28.50, y=31.00, z=176.50], rn['Bat'/848607, l='MpServer', x=-106.25, y=36.10, z=133.25], rn['Bat'/855800, l='MpServer', x=-50.75, y=21.14, z=143.59], tv['Zombie'/849078, l='MpServer', x=-31.50, y=31.00, z=179.50], te['Creeper'/849080, l='MpServer', x=-26.52, y=20.00, z=164.68], rn['Bat'/855798, l='MpServer', x=-47.75, y=21.54, z=140.41], sr['item.item.egg'/791057, l='MpServer', x=-164.31, y=68.13, z=72.69], tq['Skeleton'/849081, l='MpServer', x=-30.50, y=31.00, z=179.50], te['Creeper'/839856, l='MpServer', x=-103.50, y=41.00, z=134.50], te['Creeper'/839857, l='MpServer', x=-106.25, y=41.00, z=133.06], tq['Skeleton'/840101, l='MpServer', x=-48.84, y=28.00, z=127.72], tq['Skeleton'/840100, l='MpServer', x=-147.50, y=26.00, z=63.50], tq['Skeleton'/840103, l='MpServer', x=-52.50, y=27.00, z=126.50], tq['Skeleton'/840102, l='MpServer', x=-52.50, y=27.00, z=127.34], tv['Zombie'/856875, l='MpServer', x=-67.50, y=29.00, z=162.50], tq['Skeleton'/841747, l='MpServer', x=-44.50, y=12.00, z=106.50], tv['Zombie'/856874, l='MpServer', x=-68.50, y=29.00, z=161.50], tv['Zombie'/785174, l='MpServer', x=-69.44, y=49.00, z=88.00], tq['Skeleton'/841751, l='MpServer', x=-48.25, y=11.00, z=103.78], te['Creeper'/856878, l='MpServer', x=-39.50, y=30.00, z=103.50], tq['Skeleton'/841750, l='MpServer', x=-43.50, y=12.00, z=105.50], rn['Bat'/848609, l='MpServer', x=-48.84, y=54.00, z=146.69], tq['Skeleton'/825758, l='MpServer', x=-83.50, y=22.00, z=114.91], tq['Skeleton'/825756, l='MpServer', x=-87.94, y=24.00, z=123.97], tv['Zombie'/791340, l='MpServer', x=-90.22, y=35.00, z=104.78], tq['Skeleton'/852483, l='MpServer', x=-27.50, y=25.00, z=115.50], rn['Bat'/848629, l='MpServer', x=-39.58, y=25.82, z=139.26], rn['Bat'/848630, l='MpServer', x=-43.44, y=34.00, z=134.09]]
	Retry entities: 0 total; []
	Server brand: vanilla
	Server type: Integrated singleplayer server
Stacktrace:
	at bda.a(SourceFile:284)
	at ats.b(SourceFile:1761)
	at ats.d(SourceFile:633)
	at net.minecraft.client.main.Main.main(SourceFile:101)

-- System Details --
Details:
	Minecraft Version: 1.6.2
	Operating System: Mac OS X (x86_64) version 10.7.5
	Java Version: 1.6.0_51, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 135802112 bytes (129 MB) / 498708480 bytes (475 MB) up to 1069416448 bytes (1019 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 2633 (147448 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 1, tallocated: 63
	Launched Version: 1.6.2
	LWJGL: 2.9.0
	OpenGL: Intel GMA 950 OpenGL Engine GL version 1.4 APPLE-7.4.1, Intel Inc.
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Pack: Default
	Current Language: English (US)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 2814 (157584 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used