Hopper: java.util.ConcurrentModificationException (SourceFile:69)

This is an automatically generated report based from the following crash: http://hopper.minecraft.net/crashes/minecraft/MCX-2604/

Crash:

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
	at java.util.HashMap$ValueIterator.next(Unknown Source)
	at aim.a(SourceFile:69)
	at aes.a(SourceFile:425)
	at jq.a(SourceFile:168)
	at adq.a(SourceFile:732)
	at jq.c(SourceFile:105)
	at jp.<init>(SourceFile:29)
	at jo.a(SourceFile:208)
	at jo.a(SourceFile:240)
	at hm.a(SourceFile:141)
	at hm.c(SourceFile:188)
	at hm.a(SourceFile:85)
	at bkz.b(SourceFile:73)
	at net.minecraft.server.MinecraftServer.t(SourceFile:488)
	at net.minecraft.server.MinecraftServer.s(SourceFile:405)
	at bkw.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:339)
	at hh.run(SourceFile:582)

The following is the first clean report made public about this crash:

---- Minecraft Crash Report ----
// I let you down. Sorry :(

Time: 02/08/13 17:13
Description: Exception in server tick loop

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
	at java.util.HashMap$ValueIterator.next(Unknown Source)
	at aim.a(SourceFile:69)
	at aes.a(SourceFile:425)
	at jq.a(SourceFile:168)
	at adq.a(SourceFile:732)
	at jq.c(SourceFile:105)
	at jp.<init>(SourceFile:29)
	at jo.a(SourceFile:208)
	at jo.a(SourceFile:240)
	at hm.a(SourceFile:141)
	at hm.c(SourceFile:188)
	at hm.a(SourceFile:85)
	at bkz.b(SourceFile:73)
	at net.minecraft.server.MinecraftServer.t(SourceFile:488)
	at net.minecraft.server.MinecraftServer.s(SourceFile:405)
	at bkw.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:339)
	at hh.run(SourceFile:582)


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

-- System Details --
Details:
	Minecraft Version: 1.6.2
	Operating System: Windows Vista (x86) version 6.0
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 69963992 bytes (66 MB) / 201764864 bytes (192 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
	AABB Pool Size: 6646 (372176 bytes; 0 MB) allocated, 6646 (372176 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: 961 (53816 bytes; 0 MB) allocated, 961 (53816 bytes; 0 MB) used
	Player Count: 1 / 8; [ju['TrickCthul'/1022, l='Trickster's Den', x=1330.78, y=81.48, z=163.82]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.

You can see this full report at http://hopper.minecraft.net/crashes/minecraft/MCX-2604/52963/