Hopper: java.lang.ClassCastException: wu cannot be cast to bam

java.lang.ClassCastException: wu cannot be cast to bam
	at bak.a(SourceFile:176)
	at azw.a(SourceFile:595)
	at bak.a(SourceFile:313)
	at ayw.n(SourceFile:164)
	at ayw.m(SourceFile:116)

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

Time: 9/7/13 1:52 AM
Description: Updating screen events

java.lang.ClassCastException: wu cannot be cast to bam
	at bak.a(SourceFile:176)
	at azw.a(SourceFile:595)
	at bak.a(SourceFile:313)
	at ayw.n(SourceFile:164)
	at ayw.m(SourceFile:116)
	at awb.m(SourceFile:1202)
	at awb.V(SourceFile:686)
	at awb.e(SourceFile:642)
	at net.minecraft.client.main.Main.main(SourceFile:103)


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

-- Head --
Stacktrace:
	at bak.a(SourceFile:176)
	at azw.a(SourceFile:595)
	at bak.a(SourceFile:313)
	at ayw.n(SourceFile:164)
	at ayw.m(SourceFile:116)

-- Affected screen --
Details:
	Screen name: ~~ERROR~~ NullPointerException: null

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bfn['Player'/3544337, l='MpServer', x=53.72, y=65.62, z=-162.39]]
	Chunk stats: MultiplayerChunkCache: 312, 312
	Level seed: 0
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn location: World: (-20,64,-60), Chunk: (at 12,4,4 in -2,-4; contains blocks -32,0,-64 to -17,255,-49), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
	Level time: 1100 game time, 1100 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: creative (ID 1). Hardcore: false. Cheats: false
	Forced entities: 63 total; [tj['item.item.seeds'/3547707, l='MpServer', x=-8.84, y=65.13, z=-146.22], un['Zombie'/3545818, l='MpServer', x=6.50, y=45.00, z=-239.50], un['Zombie'/3545820, l='MpServer', x=1.97, y=44.00, z=-241.47], tw['Creeper'/3544879, l='MpServer', x=16.50, y=22.00, z=-89.91], un['Zombie'/3546104, l='MpServer', x=48.17, y=29.00, z=-224.62], bfn['Player'/3544337, l='MpServer', x=53.72, y=65.62, z=-162.39], un['Zombie'/3544883, l='MpServer', x=16.91, y=20.00, z=-94.38], tw['Creeper'/3544881, l='MpServer', x=11.50, y=20.00, z=-93.50], tw['Creeper'/3544880, l='MpServer', x=14.50, y=20.00, z=-93.50], sn['Pig'/3544189, l='MpServer', x=-19.50, y=65.00, z=-242.91], un['Zombie'/3546014, l='MpServer', x=90.50, y=33.00, z=-220.50], so['Sheep'/3544191, l='MpServer', x=-22.50, y=66.00, z=-112.50], un['Zombie'/3546015, l='MpServer', x=85.94, y=33.00, z=-221.47], ui['Skeleton'/3544921, l='MpServer', x=-3.09, y=37.00, z=-156.44], ui['Skeleton'/3544922, l='MpServer', x=0.50, y=37.00, z=-150.50], sd['Bat'/3544160, l='MpServer', x=-22.27, y=26.05, z=-119.97], un['Zombie'/3546314, l='MpServer', x=3.50, y=31.00, z=-238.50], un['Zombie'/3544957, l='MpServer', x=92.34, y=33.00, z=-217.66], un['Zombie'/3544956, l='MpServer', x=91.50, y=33.00, z=-216.50], un['Zombie'/3544734, l='MpServer', x=-16.50, y=48.00, z=-122.50], tw['Creeper'/3546145, l='MpServer', x=-3.50, y=24.00, z=-93.50], un['Zombie'/3544735, l='MpServer', x=-14.50, y=48.00, z=-122.50], tw['Creeper'/3544732, l='MpServer', x=-25.50, y=25.00, z=-122.50], tw['Creeper'/3544733, l='MpServer', x=-25.50, y=25.00, z=-123.50], sn['Pig'/3544251, l='MpServer', x=21.50, y=68.00, z=-153.50], sn['Pig'/3544252, l='MpServer', x=20.50, y=68.00, z=-155.50], tw['Creeper'/3544731, l='MpServer', x=-26.50, y=25.00, z=-122.50], sn['Pig'/3544253, l='MpServer', x=20.50, y=68.00, z=-157.50], sn['Pig'/3544254, l='MpServer', x=18.50, y=68.00, z=-157.50], un['Zombie'/3544224, l='MpServer', x=14.50, y=23.00, z=-86.50], ui['Skeleton'/3544999, l='MpServer', x=7.50, y=40.00, z=-84.50], ui['Skeleton'/3544208, l='MpServer', x=-10.50, y=27.00, z=-85.50], so['Sheep'/3544219, l='MpServer', x=8.50, y=67.00, z=-164.47], tj['item.item.seeds'/3547798, l='MpServer', x=-5.66, y=67.19, z=-147.31], so['Sheep'/3544222, l='MpServer', x=8.50, y=67.00, z=-165.81], un['Zombie'/3544223, l='MpServer', x=1.50, y=60.00, z=-111.50], so['Sheep'/3544220, l='MpServer', x=10.50, y=67.00, z=-166.22], so['Sheep'/3544221, l='MpServer', x=5.03, y=68.00, z=-166.84], tw['Creeper'/3545715, l='MpServer', x=3.50, y=48.00, z=-84.50], tw['Creeper'/3545716, l='MpServer', x=4.50, y=48.00, z=-84.50], so['Sheep'/3544203, l='MpServer', x=-10.16, y=67.00, z=-122.38], un['Zombie'/3544202, l='MpServer', x=-9.22, y=47.00, z=-116.13], tw['Creeper'/3544207, l='MpServer', x=-5.50, y=38.00, z=-96.50], so['Sheep'/3544206, l='MpServer', x=-9.16, y=66.00, z=-120.13], so['Sheep'/3544205, l='MpServer', x=-5.97, y=66.00, z=-117.06], so['Sheep'/3544204, l='MpServer', x=-12.19, y=67.00, z=-123.38], sr['Squid'/3544304, l='MpServer', x=65.91, y=45.38, z=-112.28], sr['Squid'/3544288, l='MpServer', x=59.44, y=57.66, z=-111.50], sr['Squid'/3544301, l='MpServer', x=65.72, y=46.94, z=-108.75], sr['Squid'/3544303, l='MpServer', x=64.69, y=48.34, z=-108.38], sr['Squid'/3544302, l='MpServer', x=66.56, y=48.38, z=-121.75], sd['Bat'/3545633, l='MpServer', x=24.52, y=30.97, z=-237.83], so['Sheep'/3544272, l='MpServer', x=30.34, y=70.00, z=-91.50], sd['Bat'/3544824, l='MpServer', x=63.22, y=41.17, z=-171.50], sd['Bat'/3544825, l='MpServer', x=70.53, y=40.57, z=-171.23], sr['Squid'/3544287, l='MpServer', x=51.81, y=59.16, z=-126.78], sd['Bat'/3544826, l='MpServer', x=8.35, y=11.67, z=-88.05], sd['Bat'/3545641, l='MpServer', x=39.65, y=36.78, z=-220.17], sd['Bat'/3545643, l='MpServer', x=39.98, y=37.12, z=-214.33], sr['Squid'/3544269, l='MpServer', x=51.09, y=49.78, z=-103.47], sr['Squid'/3544267, l='MpServer', x=48.81, y=59.31, z=-127.84], sr['Squid'/3544266, l='MpServer', x=37.56, y=59.31, z=-129.41], sr['Squid'/3544265, l='MpServer', x=45.14, y=52.27, z=-131.07]]
	Retry entities: 0 total; []
	Server brand: vanilla
	Server type: Integrated singleplayer server
Stacktrace:
	at bfi.a(SourceFile:285)
	at awb.b(SourceFile:1813)
	at awb.e(SourceFile:651)
	at net.minecraft.client.main.Main.main(SourceFile:103)

-- System Details --
Details:
	Minecraft Version: 13w36b
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_21, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 13561120 bytes (12 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: 17977 (1006712 bytes; 0 MB) allocated, 2 (112 bytes; 0 MB) used
	IntCache: cache: 1, tcache: 1, allocated: 12, tallocated: 94
	Launched Version: 13w36b
	LWJGL: 2.9.0
	OpenGL: ATI Radeon 3100 Graphics GL version 3.3.11161 Compatibility Profile Context, ATI Technologies Inc.
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Packs: [RedstonePak v1.1-1.6.zip]
	Current Language: English (US)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 37007 (2072392 bytes; 1 MB) allocated, 17 (952 bytes; 0 MB) used