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

This is an automatically generated report based from the following crash: http://hopper.minecraft.net/crashes/minecraft/MCX-190508/

Crash:

java.lang.ClassCastException: cf cannot be cast to cj
	at by.d(SourceFile:120)
	at ye.a(SourceFile:439)
	at awy.a(SourceFile:188)
	at awy.a(SourceFile:168)
	at bfe.b(SourceFile:718)
	at atv.S(SourceFile:686)
	at atv.d(SourceFile:619)
	at net.minecraft.client.main.Main.main(SourceFile:101)

The following is the first clean report made public about this crash:

---- Minecraft Crash Report ----
// My bad.

Time: 9/19/13 4:18 PM
Description: Reading NBT data

java.lang.ClassCastException: cf cannot be cast to cj
	at by.d(SourceFile:120)
	at ye.a(SourceFile:439)
	at awy.a(SourceFile:188)
	at awy.a(SourceFile:168)
	at bfe.b(SourceFile:718)
	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: SHORT
	Tag name: id
Stacktrace:
	at by.d(SourceFile:120)
	at ye.a(SourceFile:439)
	at awy.a(SourceFile:188)
	at awy.a(SourceFile:168)

-- Screen render details --
Details:
	Screen name: axj
	Mouse location: Scaled: (202, 102). Absolute: (405, 274)
	Screen size: Scaled: (427, 240). Absolute: (854, 480). Scale factor of 2

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bdi['Chickenfuzzywing'/154961, l='MpServer', x=722.55, y=5.62, z=445.83]]
	Chunk stats: MultiplayerChunkCache: 441
	Level seed: 0
	Level generator: ID 01 - flat, ver 0. Features enabled: false
	Level generator options: 
	Level spawn location: World: (733,4,444), Chunk: (at 13,0,12 in 45,27; contains blocks 720,0,432 to 735,255,447), Region: (1,0; contains chunks 32,0 to 63,31, blocks 512,0,0 to 1023,255,511)
	Level time: 169910 game time, 8267 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: 9 total; [rz['Sheep'/154953, l='MpServer', x=748.81, y=4.00, z=498.78], rz['Sheep'/154952, l='MpServer', x=658.75, y=4.00, z=450.88], rz['Sheep'/154955, l='MpServer', x=760.38, y=4.00, z=491.78], rz['Sheep'/154954, l='MpServer', x=756.19, y=4.00, z=476.84], rz['Sheep'/154956, l='MpServer', x=756.50, y=4.00, z=487.50], rz['Sheep'/154949, l='MpServer', x=666.22, y=4.00, z=426.22], bdi['Chickenfuzzywing'/154961, l='MpServer', x=722.55, y=5.62, z=445.83], rz['Sheep'/154951, l='MpServer', x=656.16, y=4.00, z=439.91], rz['Sheep'/154950, l='MpServer', x=669.31, y=4.00, z=441.78]]
	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: Mac OS X (x86_64) version 10.8.4
	Java Version: 1.6.0_51, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 191663272 bytes (182 MB) / 462573568 bytes (441 MB) up to 1069416448 bytes (1019 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 19635 (1099560 bytes; 1 MB) allocated, 180 (10080 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Launched Version: 1.6.4
	LWJGL: 2.9.0
	OpenGL: NVIDIA GeForce 9400 OpenGL Engine GL version 2.1 NVIDIA-8.12.47 310.40.00.05f01, NVIDIA Corporation
	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: 309 (17304 bytes; 0 MB) allocated, 69 (3864 bytes; 0 MB) used

You can see this full report at http://hopper.minecraft.net/crashes/minecraft/MCX-190508/12430370/