Hopper: java.lang.NullPointerException

java.lang.NullPointerException
	at aci.a(SourceFile:71)
	at js.b(SourceFile:107)

---- Minecraft Crash Report ----
// I bet Cylons wouldn't have this problem.

Time: 9/19/13 6:10 PM
Description: Exception ticking world

java.lang.ClassCastException: <unknown> cannot be cast to java.lang.Boolean
	at aci.a(SourceFile:71)
	at js.b(SourceFile:107)
	at net.minecraft.server.MinecraftServer.t(SourceFile:463)
	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 aci.a(SourceFile:71)
	at js.b(SourceFile:107)

-- Affected level --
Details:
	Level name: survive
	All players: 1 total; [jv['RyGuy28lax'/57, l='survive', x=469.15, y=5.79, z=-331.59]]
	Chunk stats: ServerChunkCache: 899 Drop: 0
	Level seed: 1361820374256379026
	Level generator: ID 00 - default, ver 1. Features enabled: true
	Level generator options: 
	Level spawn location: World: (492,4,-588), Chunk: (at 12,0,4 in 30,-37; contains blocks 480,0,-592 to 495,255,-577), Region: (0,-2; contains chunks 0,-64 to 31,-33, blocks 0,0,-1024 to 511,255,-513)
	Level time: 1214396 game time, 1241053 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 153984 (now: false), thunder time: 9917 (now: false)
	Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: true
Stacktrace:
	at net.minecraft.server.MinecraftServer.t(SourceFile:463)
	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: Windows Vista (x86) version 6.0
	Java Version: 1.7.0_09, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
	Memory: 251436296 bytes (239 MB) / 518979584 bytes (494 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
	AABB Pool Size: 692 (38752 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
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 81 (4536 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	Player Count: 1 / 8; [jv['RyGuy28lax'/57, l='survive', x=469.15, y=5.79, z=-331.59]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.