Random Crash

Put the summary of the bug you're having here

What I expected to happen was...:
Minecraft run as normal

What actually happened was...:
My minecraft gave me the following error:
---- Minecraft Crash Report ----
// Don't be sad. I'll do better next time, I promise!

Time: 7/4/13 10:58 AM
Description: Unexpected error

java.lang.ClassCastException: arr cannot be cast to ary
at anw.a(SourceFile:81)
at bct.a(SourceFile:233)
at atn.c(SourceFile:1058)
at atn.k(SourceFile:1344)
at atn.S(SourceFile:662)
at atn.d(SourceFile:618)
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 anw.a(SourceFile:81)
at bct.a(SourceFile:233)
at atn.c(SourceFile:1058)

– Affected level –
Details:
Level name: MpServer
All players: 10 total; [bcx['RobertWebb38'/112, l='MpServer', x=-22.45, y=46.62, z=261.79], ben['Caorti'/111, l='MpServer', x=1.25, y=46.00, z=271.53], ben['jabadencio'/106, l='MpServer', x=18.50, y=52.00, z=238.31], ben['peloc81'/103, l='MpServer', x=-17.83, y=53.00, z=286.15], ben['markie1234'/108, l='MpServer', x=7.60, y=56.00, z=248.69], ben['phvikings12'/113, l='MpServer', x=-19.53, y=48.68, z=244.01], ben['TNT777777'/114, l='MpServer', x=32.22, y=41.00, z=267.72], ben['ferosidademaxi'/109, l='MpServer', x=-9.00, y=46.00, z=246.10], ben['hawkp'/105, l='MpServer', x=-8.31, y=53.00, z=272.00], ben['jjyunes'/207, l='MpServer', x=-9.63, y=46.00, z=248.13]]
Chunk stats: MultiplayerChunkCache: 121
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: World: (-6,51,257), Chunk: (at 10,3,1 in -1,16; contains blocks -16,0,256 to -1,255,271), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Level time: 24148889 game time, 28537104 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: adventure (ID 2). Hardcore: false. Cheats: false
Forced entities: 103 total; [ben['peloc81'/103, l='MpServer', x=-17.83, y=53.00, z=286.15], ben['Caorti'/111, l='MpServer', x=1.25, y=46.00, z=271.53], ben['markie1234'/108, l='MpServer', x=7.60, y=56.00, z=248.69], ben['ferosidademaxi'/109, l='MpServer', x=-9.00, y=46.00, z=246.10], ben['jabadencio'/106, l='MpServer', x=18.50, y=52.00, z=238.31], ben['hawkp'/105, l='MpServer', x=-8.31, y=53.00, z=272.00], ben['TNT777777'/114, l='MpServer', x=32.22, y=41.00, z=267.72], ben['phvikings12'/113, l='MpServer', x=-19.53, y=48.68, z=244.01], oa['entity.ItemFrame.name'/127, l='MpServer', x=-33.94, y=35.50, z=264.50], oa['entity.ItemFrame.name'/126, l='MpServer', x=-33.94, y=36.50, z=263.50], oa['entity.ItemFrame.name'/125, l='MpServer', x=-33.94, y=35.50, z=263.50], oa['entity.ItemFrame.name'/124, l='MpServer', x=-33.94, y=34.50, z=263.50], oa['entity.ItemFrame.name'/123, l='MpServer', x=-33.94, y=33.50, z=263.50], oa['entity.ItemFrame.name'/122, l='MpServer', x=-33.94, y=34.50, z=255.50], oa['entity.ItemFrame.name'/121, l='MpServer', x=-33.94, y=35.50, z=255.50], oa['entity.ItemFrame.name'/137, l='MpServer', x=-32.94, y=35.50, z=260.50], oa['entity.ItemFrame.name'/136, l='MpServer', x=-32.50, y=35.50, z=265.94], oa['entity.ItemFrame.name'/139, l='MpServer', x=-32.94, y=36.50, z=259.50], oa['entity.ItemFrame.name'/138, l='MpServer', x=-32.94, y=36.50, z=260.50], sv['entity.MinecartRideable.name'/141, l='MpServer', x=-30.06, y=45.50, z=260.88], oa['entity.ItemFrame.name'/140, l='MpServer', x=-32.94, y=35.50, z=259.50], oa['entity.ItemFrame.name'/143, l='MpServer', x=-28.50, y=33.50, z=254.06], oa['entity.ItemFrame.name'/142, l='MpServer', x=-29.50, y=33.50, z=254.06], oa['entity.ItemFrame.name'/129, l='MpServer', x=-33.94, y=35.50, z=262.50], oa['entity.ItemFrame.name'/128, l='MpServer', x=-33.94, y=34.50, z=264.50], oa['entity.ItemFrame.name'/131, l='MpServer', x=-33.94, y=33.50, z=256.50], oa['entity.ItemFrame.name'/130, l='MpServer', x=-33.94, y=34.50, z=262.50], oa['entity.ItemFrame.name'/133, l='MpServer', x=-33.94, y=35.50, z=256.50], oa['entity.ItemFrame.name'/132, l='MpServer', x=-33.94, y=34.50, z=256.50], oa['entity.ItemFrame.name'/135, l='MpServer', x=-33.94, y=34.50, z=257.50], oa['entity.ItemFrame.name'/134, l='MpServer', x=-33.94, y=35.50, z=257.50], oa['entity.ItemFrame.name'/152, l='MpServer', x=-31.50, y=34.50, z=254.06], oa['entity.ItemFrame.name'/153, l='MpServer', x=-26.50, y=34.50, z=265.94], oa['entity.ItemFrame.name'/154, l='MpServer', x=-27.50, y=35.50, z=265.94], oa['entity.ItemFrame.name'/155, l='MpServer', x=-30.50, y=35.50, z=265.94], oa['entity.ItemFrame.name'/156, l='MpServer', x=-31.50, y=34.50, z=265.94], oa['entity.ItemFrame.name'/157, l='MpServer', x=-26.50, y=33.50, z=265.94], oa['entity.ItemFrame.name'/158, l='MpServer', x=-26.50, y=32.50, z=265.94], oa['entity.ItemFrame.name'/159, l='MpServer', x=-31.50, y=32.50, z=265.94], oa['entity.ItemFrame.name'/144, l='MpServer', x=-29.50, y=36.50, z=254.06], oa['entity.ItemFrame.name'/145, l='MpServer', x=-29.50, y=34.50, z=254.06], oa['entity.ItemFrame.name'/146, l='MpServer', x=-28.50, y=36.50, z=254.06], oa['entity.ItemFrame.name'/147, l='MpServer', x=-30.50, y=35.50, z=254.06], oa['entity.ItemFrame.name'/148, l='MpServer', x=-30.50, y=34.50, z=254.06], oa['entity.ItemFrame.name'/149, l='MpServer', x=-27.50, y=35.50, z=254.06], oa['entity.ItemFrame.name'/150, l='MpServer', x=-26.50, y=35.50, z=254.06], oa['entity.ItemFrame.name'/151, l='MpServer', x=-26.50, y=34.50, z=254.06], oa['entity.ItemFrame.name'/171, l='MpServer', x=-24.06, y=35.50, z=262.50], oa['entity.ItemFrame.name'/170, l='MpServer', x=-24.06, y=34.50, z=262.50], oa['entity.ItemFrame.name'/169, l='MpServer', x=-24.06, y=33.50, z=262.50], oa['entity.ItemFrame.name'/168, l='MpServer', x=-24.06, y=36.50, z=257.50], oa['entity.ItemFrame.name'/175, l='MpServer', x=-24.06, y=35.50, z=261.50], oa['entity.ItemFrame.name'/174, l='MpServer', x=-24.06, y=34.50, z=258.50], oa['entity.ItemFrame.name'/173, l='MpServer', x=-24.06, y=35.50, z=258.50], oa['entity.ItemFrame.name'/172, l='MpServer', x=-24.06, y=36.50, z=262.50], oa['entity.ItemFrame.name'/163, l='MpServer', x=-25.50, y=35.50, z=265.94], oa['entity.ItemFrame.name'/162, l='MpServer', x=-31.50, y=36.50, z=265.94], oa['entity.ItemFrame.name'/161, l='MpServer', x=-26.50, y=36.50, z=265.94], oa['entity.ItemFrame.name'/160, l='MpServer', x=-31.50, y=33.50, z=265.94], oa['entity.ItemFrame.name'/167, l='MpServer', x=-24.06, y=33.50, z=257.50], oa['entity.ItemFrame.name'/166, l='MpServer', x=-24.06, y=34.50, z=257.50], oa['entity.ItemFrame.name'/165, l='MpServer', x=-24.06, y=35.50, z=257.50], oa['entity.ItemFrame.name'/164, l='MpServer', x=-30.50, y=37.50, z=265.94], oa['entity.ItemFrame.name'/186, l='MpServer', x=13.94, y=52.50, z=252.50], oa['entity.ItemFrame.name'/187, l='MpServer', x=13.94, y=52.50, z=251.50], oa['entity.ItemFrame.name'/184, l='MpServer', x=-24.06, y=33.50, z=260.50], oa['entity.ItemFrame.name'/185, l='MpServer', x=13.94, y=53.50, z=252.50], oi['Painting'/190, l='MpServer', x=10.50, y=54.00, z=253.94], oa['entity.ItemFrame.name'/191, l='MpServer', x=25.50, y=55.50, z=277.06], oa['entity.ItemFrame.name'/188, l='MpServer', x=13.94, y=54.50, z=253.50], oa['entity.ItemFrame.name'/189, l='MpServer', x=13.94, y=53.50, z=253.50], oa['entity.ItemFrame.name'/178, l='MpServer', x=-24.06, y=34.50, z=256.50], oa['entity.ItemFrame.name'/179, l='MpServer', x=-24.06, y=35.50, z=263.50], oa['entity.ItemFrame.name'/176, l='MpServer', x=-24.06, y=34.50, z=261.50], oa['entity.ItemFrame.name'/177, l='MpServer', x=-24.06, y=35.50, z=256.50], oa['entity.ItemFrame.name'/182, l='MpServer', x=-24.06, y=36.50, z=260.50], oa['entity.ItemFrame.name'/183, l='MpServer', x=-24.06, y=33.50, z=259.50], oa['entity.ItemFrame.name'/180, l='MpServer', x=-24.06, y=34.50, z=263.50], oa['entity.ItemFrame.name'/181, l='MpServer', x=-24.06, y=36.50, z=259.50], ben['jjyunes'/207, l='MpServer', x=-9.63, y=46.00, z=248.13], oa['entity.ItemFrame.name'/201, l='MpServer', x=26.50, y=56.50, z=288.94], oa['entity.ItemFrame.name'/200, l='MpServer', x=25.50, y=56.50, z=288.94], oa['entity.ItemFrame.name'/202, l='MpServer', x=27.50, y=56.50, z=288.94], oa['entity.ItemFrame.name'/197, l='MpServer', x=27.50, y=55.50, z=288.94], oa['entity.ItemFrame.name'/196, l='MpServer', x=25.50, y=56.50, z=277.06], oa['entity.ItemFrame.name'/199, l='MpServer', x=26.50, y=55.50, z=288.94], oa['entity.ItemFrame.name'/198, l='MpServer', x=25.50, y=55.50, z=288.94], oa['entity.ItemFrame.name'/193, l='MpServer', x=27.50, y=55.50, z=277.06], oa['entity.ItemFrame.name'/192, l='MpServer', x=26.50, y=55.50, z=277.06], oa['entity.ItemFrame.name'/195, l='MpServer', x=26.50, y=56.50, z=277.06], oa['entity.ItemFrame.name'/194, l='MpServer', x=27.50, y=56.50, z=277.06], ben['TNT777777'/114, l='MpServer', x=32.22, y=41.00, z=267.72], ben['phvikings12'/113, l='MpServer', x=-19.53, y=48.68, z=244.01], ben['markie1234'/108, l='MpServer', x=7.60, y=56.00, z=248.69], ben['peloc81'/103, l='MpServer', x=-17.83, y=53.00, z=286.15], ben['jabadencio'/106, l='MpServer', x=18.50, y=52.00, z=238.31], ben['felipegnbr'/104, l='MpServer', x=-6.00, y=51.00, z=257.00], ben['Caorti'/111, l='MpServer', x=1.25, y=46.00, z=271.53], ben['jjyunes'/207, l='MpServer', x=-9.63, y=46.00, z=248.13], ben['hawkp'/105, l='MpServer', x=-8.31, y=53.00, z=272.00], ben['ferosidademaxi'/109, l='MpServer', x=-9.00, y=46.00, z=246.10], oi['Painting'/190, l='MpServer', x=10.50, y=54.00, z=253.94], bcx['RobertWebb38'/112, l='MpServer', x=-22.45, y=46.62, z=261.79]]
Retry entities: 0 total; []
Stacktrace:
at bcu.a(SourceFile:284)
at atn.b(SourceFile:1743)
at atn.d(SourceFile:632)
at net.minecraft.client.main.Main.main(SourceFile:101)

– System Details –
Details:
Minecraft Version: 1.6.1
Operating System: Mac OS X (x86_64) version 10.8.4
Java Version: 1.6.0_45, Apple Inc.
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
Memory: 91895888 bytes (87 MB) / 147406848 bytes (140 MB) up to 1065025536 bytes (1015 MB)
JVM Flags: 1 total; -Xmx1G
AABB Pool Size: 13873 (776888 bytes; 0 MB) allocated, 2 (112 bytes; 0 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 63
Launched Version: 1.6.1
LWJGL: 2.9.0
OpenGL: AMD Radeon HD 6770M OpenGL Engine GL version 2.1 ATI-1.8.18, ATI Technologies Inc.
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Pack: TexturePak1.zip
Profiler Position: N/A (disabled)
Vec3 Pool Size: 834 (46704 bytes; 0 MB) allocated, 16 (896 bytes; 0 MB) used

Steps to Reproduce:
Not sure