Hopper: java.lang.ArrayIndexOutOfBoundsException: -1

java.lang.ArrayIndexOutOfBoundsException: -1
	at java.util.ArrayList.fastRemove(ArrayList.java:441)
	at java.util.ArrayList.remove(ArrayList.java:424)
	at jq.b(SourceFile:52)
	at jp.c(SourceFile:302)
	at hn.e(SourceFile:211)
	at ka.a(SourceFile:398)
	at cn.b(SourceFile:72)
	at ka.e(SourceFile:60)

---- Minecraft Crash Report ----
// Oh - I know what I did wrong!

Time: 9/20/13 7:21 PM
Description: Ticking memory connection

java.lang.ArrayIndexOutOfBoundsException: -1
	at java.util.ArrayList.fastRemove(ArrayList.java:441)
	at java.util.ArrayList.remove(ArrayList.java:424)
	at jq.b(SourceFile:52)
	at jp.c(SourceFile:302)
	at hn.e(SourceFile:211)
	at ka.a(SourceFile:398)
	at cn.b(SourceFile:72)
	at ka.e(SourceFile:60)
	at kd.b(SourceFile:37)
	at blc.b(SourceFile:84)
	at net.minecraft.server.MinecraftServer.t(SourceFile:489)
	at net.minecraft.server.MinecraftServer.s(SourceFile:406)
	at bkz.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:340)
	at hi.run(SourceFile:583)


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

-- Head --
Stacktrace:
	at java.util.ArrayList.fastRemove(ArrayList.java:441)
	at java.util.ArrayList.remove(ArrayList.java:424)
	at jq.b(SourceFile:52)
	at jp.c(SourceFile:302)
	at hn.e(SourceFile:211)
	at ka.a(SourceFile:398)
	at cn.b(SourceFile:72)
	at ka.e(SourceFile:60)

-- Ticking connection --
Details:
	Connection: ka@20e0b1d6
Stacktrace:
	at kd.b(SourceFile:37)
	at blc.b(SourceFile:84)
	at net.minecraft.server.MinecraftServer.t(SourceFile:489)
	at net.minecraft.server.MinecraftServer.s(SourceFile:406)
	at bkz.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:340)
	at hi.run(SourceFile:583)

-- System Details --
Details:
	Minecraft Version: 1.6.4
	Operating System: Mac OS X (x86_64) version 10.6.8
	Java Version: 1.6.0_51, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 85537952 bytes (81 MB) / 241549312 bytes (230 MB) up to 1069416448 bytes (1019 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 2437 (136472 bytes; 0 MB) allocated, 2238 (125328 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 1, tcache: 0, allocated: 3, tallocated: 63
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 3531 (197736 bytes; 0 MB) allocated, 3209 (179704 bytes; 0 MB) used
	Player Count: 0 / 8; []
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.