Crash: Exception ticking world 'java.util.ConcurrentModificationException'

---- Minecraft Crash Report ----
// Uh... Did I do that?

Time: 08-12-16 19:00
Description: Exception ticking world

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.remove(Unknown Source)
	at lv.d(SourceFile:198)
	at lw.d(SourceFile:201)
	at net.minecraft.server.MinecraftServer.D(SourceFile:626)
	at lh.D(SourceFile:335)
	at net.minecraft.server.MinecraftServer.C(SourceFile:562)
	at net.minecraft.server.MinecraftServer.run(SourceFile:466)
	at java.lang.Thread.run(Unknown Source)


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

-- Head --
Thread: Server thread
Stacktrace:
	at java.util.HashMap$HashIterator.remove(Unknown Source)
	at lv.d(SourceFile:198)
	at lw.d(SourceFile:201)

-- Affected level --
Details:
	Level name: ardata
	All players: 0 total; []
	Chunk stats: ServerChunkCache: 471 Drop: 216
	Level seed: -594370370092952685
	Level generator: ID 00 - default, ver 1. Features enabled: true
	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: 218573667 game time, 220574350 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 122951 (now: false), thunder time: 45617 (now: false)
	Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
Stacktrace:
	at net.minecraft.server.MinecraftServer.D(SourceFile:626)
	at lh.D(SourceFile:335)
	at net.minecraft.server.MinecraftServer.C(SourceFile:562)
	at net.minecraft.server.MinecraftServer.run(SourceFile:466)
	at java.lang.Thread.run(Unknown Source)

-- System Details --
Details:
	Minecraft Version: 1.11
	Operating System: Windows Server 2012 R2 (amd64) version 6.3
	Java Version: 1.8.0_111, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 3143403160 bytes (2997 MB) / 4246732800 bytes (4050 MB) up to 4246732800 bytes (4050 MB)
	JVM Flags: 2 total; -Xmx4G -Xms4G
	IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
	Profiler Position: N/A (disabled)
	Player Count: 0 / 60; []
	Is Modded: Unknown (can't tell)
	Type: Dedicated Server (map_server.txt)