Hopper: java.lang.ClassCastException: we cannot be cast to axo

java.lang.ClassCastException: we cannot be cast to axo
	at axm.a(SourceFile:177)
	at awy.a(SourceFile:447)
	at awe.d(SourceFile:135)
	at axm.d(SourceFile:488)
	at awe.m(SourceFile:107)

---- Minecraft Crash Report ----
// I feel sad now :(

Time: 9/21/13 8:15 AM
Description: Updating screen events

java.lang.ClassCastException: we cannot be cast to axo
	at axm.a(SourceFile:177)
	at awy.a(SourceFile:447)
	at awe.d(SourceFile:135)
	at axm.d(SourceFile:488)
	at awe.m(SourceFile:107)
	at atv.k(SourceFile:1158)
	at atv.S(SourceFile:663)
	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:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
	at axm.a(SourceFile:177)
	at awy.a(SourceFile:447)
	at awe.d(SourceFile:135)
	at axm.d(SourceFile:488)
	at awe.m(SourceFile:107)

-- Affected screen --
Details:
	Screen name: axm

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bdi['Austin6216'/79, l='MpServer', x=-752.25, y=77.90, z=576.66]]
	Chunk stats: MultiplayerChunkCache: 441
	Level seed: 0
	Level generator: ID 01 - flat, ver 0. Features enabled: false
	Level generator options: 
	Level spawn location: World: (-855,4,323), Chunk: (at 9,0,3 in -54,20; contains blocks -864,0,320 to -849,255,335), Region: (-2,0; contains chunks -64,0 to -33,31, blocks -1024,0,0 to -513,255,511)
	Level time: 69941 game time, 69941 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: 18 total; [ro['Bat'/236205, l='MpServer', x=-689.25, y=39.10, z=653.75], ub['Villager'/63, l='MpServer', x=-759.43, y=65.00, z=583.41], uh['arrow'/235358, l='MpServer', x=-752.09, y=71.03, z=576.16], ub['Villager'/68, l='MpServer', x=-772.69, y=65.00, z=600.50], ub['Villager'/70, l='MpServer', x=-784.31, y=65.00, z=589.78], ub['Villager'/64, l='MpServer', x=-785.47, y=65.00, z=589.44], ub['Villager'/65, l='MpServer', x=-770.51, y=65.00, z=591.66], ub['Villager'/66, l='MpServer', x=-784.72, y=65.00, z=588.56], ub['Villager'/67, l='MpServer', x=-771.78, y=65.00, z=600.44], ro['Bat'/230943, l='MpServer', x=-686.88, y=38.10, z=653.53], ro['Bat'/230941, l='MpServer', x=-681.88, y=39.10, z=653.97], ub['Villager'/72, l='MpServer', x=-778.63, y=64.52, z=596.31], ro['Bat'/236405, l='MpServer', x=-677.00, y=38.20, z=655.06], ub['Villager'/74, l='MpServer', x=-779.69, y=63.22, z=596.31], ub['Villager'/75, l='MpServer', x=-785.66, y=65.00, z=590.69], bdi['Austin6216'/79, l='MpServer', x=-752.25, y=77.90, z=576.66], sc['Squid'/233114, l='MpServer', x=-779.06, y=54.22, z=597.47], ss['item.tile.torch'/199520, l='MpServer', x=-756.88, y=64.13, z=566.91]]
	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 10.6.8
	Java Version: 1.6.0_51, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 265454744 bytes (253 MB) / 633126912 bytes (603 MB) up to 1037959168 bytes (989 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 243 (13608 bytes; 0 MB) allocated, 2 (112 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: ATI Radeon HD 2400 XT OpenGL Engine GL version 2.1 ATI-1.6.36, ATI Technologies Inc.
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Pack: Default
	Current Language: English (UK)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 153 (8568 bytes; 0 MB) allocated, 13 (728 bytes; 0 MB) used