Hopper: java.lang.ClassCastException: cf cannot be cast to bx

java.lang.ClassCastException: cf cannot be cast to bx
	at by.c(SourceFile:111)
	at nj.b(SourceFile:151)
	at yp.g(SourceFile:61)
	at yp.e(SourceFile:268)
	at ye.v(SourceFile:505)
	at bgw.b(SourceFile:335)
	at avj.a(SourceFile:731)
	at avj.a(SourceFile:120)
	at bfe.b(SourceFile:700)
	at atv.S(SourceFile:686)
	at atv.d(SourceFile:619)
	at net.minecraft.client.main.Main.main(SourceFile:101)

---- Minecraft Crash Report ----
// Hey, that tickles! Hehehe!

Time: 9/19/13 2:11 PM
Description: Reading NBT data

java.lang.ClassCastException: cf cannot be cast to bx
	at by.c(SourceFile:111)
	at nj.b(SourceFile:151)
	at yp.g(SourceFile:61)
	at yp.e(SourceFile:268)
	at ye.v(SourceFile:505)
	at bgw.b(SourceFile:335)
	at avj.a(SourceFile:731)
	at avj.a(SourceFile:120)
	at bfe.b(SourceFile:700)
	at atv.S(SourceFile:686)
	at atv.d(SourceFile:619)
	at net.minecraft.client.main.Main.main(SourceFile:101)


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

-- Corrupt NBT tag --
Details:
	Tag type found: INT
	Tag type expected: BYTE
	Tag name: Id
Stacktrace:
	at by.c(SourceFile:111)
	at nj.b(SourceFile:151)
	at yp.g(SourceFile:61)
	at yp.e(SourceFile:268)
	at ye.v(SourceFile:505)
	at bgw.b(SourceFile:335)
	at avj.a(SourceFile:731)
	at avj.a(SourceFile:120)

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bdi['BrisingrMithrim'/62811, l='MpServer', x=316.24, y=57.62, z=-420.45]]
	Chunk stats: MultiplayerChunkCache: 30
	Level seed: 0
	Level generator: ID 01 - flat, ver 0. Features enabled: false
	Level generator options: 
	Level spawn location: World: (324,4,-445), Chunk: (at 4,0,3 in 20,-28; contains blocks 320,0,-448 to 335,255,-433), Region: (0,-1; contains chunks 0,-32 to 31,-1, blocks 0,0,-512 to 511,255,-1)
	Level time: 2060339 game time, 1000 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: 2 total; [ss['item.item.bone'/62810, l='MpServer', x=323.22, y=56.13, z=-456.69], bdi['BrisingrMithrim'/62811, l='MpServer', x=316.24, y=57.62, z=-420.45]]
	Retry entities: 0 total; []
	Server brand: vanilla
	Server type: Integrated singleplayer server
Stacktrace:
	at bdd.a(SourceFile:284)
	at atv.b(SourceFile:1761)
	at atv.d(SourceFile:628)
	at net.minecraft.client.main.Main.main(SourceFile:101)

-- System Details --
Details:
	Minecraft Version: 1.6.4
	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: 216208088 bytes (206 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: 2595 (145320 bytes; 0 MB) allocated, 2595 (145320 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 63
	Launched Version: 1.6.4
	LWJGL: 2.9.0
	OpenGL: Intel(R) G41 Express Chipset GL version 2.1.0 - Build 8.15.10.2119, Intel
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Pack: Default
	Current Language: English (US)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 23 (1288 bytes; 0 MB) allocated, 23 (1288 bytes; 0 MB) used