I keep crashing while playing on the server (ip=) mc-sabotage.com

Here's my error:

Minecraft has crashed!
----------------------

Minecraft has stopped running because it encountered a problem; Unexpected error

A full error report has been saved to C:\Users\Ben\AppData\Roaming\.minecraft\crash-reports\crash-2013-01-01_14.47.50-client.txt - Please include a copy of that file (Not this screen!) if you report this crash to anyone; without it, they will not be able to help fix the crash

— BEGIN ERROR REPORT a4cec2eb --------
Full report at:
C:\Users\Ben\AppData\Roaming\.minecraft\crash-reports\crash-2013-01-01_14.47.50-client.txt
Please show that file to Mojang, NOT just this screen!

Generated 1/1/13 2:47 PM

– Head –
Stacktrace:
at bdo.a(SourceFile:38)
at bdo.a(SourceFile:13)
at bdw.a(SourceFile:103)
at bdw.a(SourceFile:96)
at bav.a(RenderGlobal.java:476)
at ban.a(EntityRenderer.java:1566)

– Affected level –
Details:
Level name: MpServer
All players: 23 total; [ays['nyihockeygirl'/70, l='MpServer', x=-7.08, y=67.64, z=-20.88], bah['rango136'/6, l='MpServer', x=-11.07, y=64.00, z=-52.96], bah['gabthepro'/7, l='MpServer', x=-24.41, y=54.00, z=16.45], bah['CaptainDiscord'/8, l='MpServer', x=30.03, y=104.00, z=3.41], bah['harryr75'/10, l='MpServer', x=11.73, y=64.27, z=-54.63], bah['chrissyboy16'/11, l='MpServer', x=55.43, y=66.00, z=34.56], bah['cooly333'/14, l='MpServer', x=26.31, y=69.22, z=3.44], bah['webkinzrocks'/17, l='MpServer', x=3.82, y=65.02, z=17.95], bah['awesomekidd28'/16, l='MpServer', x=49.42, y=66.00, z=37.67], bah['timmagamar'/20, l='MpServer', x=17.41, y=65.00, z=-54.50], bah['cblack123'/23, l='MpServer', x=-54.17, y=64.00, z=-26.88], bah['Holmtraskare'/22, l='MpServer', x=-28.31, y=68.56, z=-15.56], bah['CraZCanuck'/25, l='MpServer', x=-33.22, y=71.00, z=32.09], bah['Adamjack7890'/29, l='MpServer', x=40.54, y=65.05, z=28.75], bah['wiggleking'/31, l='MpServer', x=-35.69, y=71.46, z=30.59], bah['piepants777'/30, l='MpServer', x=-29.75, y=69.91, z=18.83], bah['Quadratkopf98'/35, l='MpServer', x=-56.59, y=64.00, z=-7.68], bah['Alexia1010'/33, l='MpServer', x=26.16, y=66.94, z=3.44], bah['u_uFishdu_u'/39, l='MpServer', x=47.53, y=65.98, z=36.85], bah['lolmonster8642'/43, l='MpServer', x=29.72, y=65.00, z=37.77], bah['xZaaap'/49, l='MpServer', x=-44.10, y=85.02, z=34.21], bah['Bossguy987'/108, l='MpServer', x=26.17, y=69.47, z=3.76], bah['BroProMaster'/106, l='MpServer', x=58.66, y=72.05, z=17.55]]
Chunk stats: MultiplayerChunkCache: 121
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: World: (0,64,-1), Chunk: (at 0,4,15 in 0,-1; contains blocks 0,0,-16 to 15,255,-1), Region: (0,-1; contains chunks 0,-32 to 31,-1, blocks 0,0,-512 to 511,255,-1)
Level time: 4878386 game time, 5768962 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: 61 total; [bah['rango136'/6, l='MpServer', x=-11.07, y=64.00, z=-52.96], bah['gabthepro'/7, l='MpServer', x=-24.41, y=54.00, z=16.45], bah['CaptainDiscord'/8, l='MpServer', x=30.03, y=104.00, z=3.41], bah['harryr75'/10, l='MpServer', x=11.73, y=64.27, z=-54.63], bah['chrissyboy16'/11, l='MpServer', x=55.43, y=66.00, z=34.56], bah['cooly333'/14, l='MpServer', x=26.31, y=69.22, z=3.44], mg['Painting'/153, l='MpServer', x=9.94, y=54.00, z=-31.00], mg['Painting'/152, l='MpServer', x=1.06, y=58.00, z=-31.00], bah['webkinzrocks'/17, l='MpServer', x=3.82, y=65.02, z=17.95], mg['Painting'/153, l='MpServer', x=9.94, y=54.00, z=-31.00], mg['Painting'/152, l='MpServer', x=1.06, y=58.00, z=-31.00], bah['awesomekidd28'/16, l='MpServer', x=49.42, y=66.00, z=37.67], mg['Painting'/154, l='MpServer', x=23.06, y=87.00, z=6.00], mg['Painting'/155, l='MpServer', x=26.00, y=87.00, z=8.94], mg['Painting'/156, l='MpServer', x=28.94, y=87.00, z=6.00], bah['timmagamar'/20, l='MpServer', x=17.41, y=65.00, z=-54.50], bah['cblack123'/23, l='MpServer', x=-54.17, y=64.00, z=-26.88], bah['Holmtraskare'/22, l='MpServer', x=-28.31, y=68.56, z=-15.56], bah['CraZCanuck'/25, l='MpServer', x=-33.22, y=71.00, z=32.09], bah['Adamjack7890'/29, l='MpServer', x=40.54, y=65.05, z=28.75], bah['wiggleking'/31, l='MpServer', x=-35.69, y=71.46, z=30.59], bah['piepants777'/30, l='MpServer', x=-29.75, y=69.91, z=18.83], bah['Quadratkopf98'/35, l='MpServer', x=-56.59, y=64.00, z=-7.68], bah['Quadratkopf98'/35, l='MpServer', x=-56.59, y=64.00, z=-7.68], bah['Alexia1010'/33, l='MpServer', x=26.16, y=66.94, z=3.44], bah['piepants777'/30, l='MpServer', x=-29.75, y=69.91, z=18.83], bah['Skipp70'/34, l='MpServer', x=18.09, y=64.00, z=55.59], bah['Alexia1010'/33, l='MpServer', x=26.16, y=66.94, z=3.44], bah['emilito15110'/28, l='MpServer', x=-17.50, y=73.00, z=55.09], bah['u_uFishdu_u'/39, l='MpServer', x=47.53, y=65.98, z=36.85], bah['wiggleking'/31, l='MpServer', x=-35.69, y=71.46, z=30.59], bah['CraZCanuck'/25, l='MpServer', x=-33.22, y=71.00, z=32.09], bah['Adamjack7890'/29, l='MpServer', x=40.54, y=65.05, z=28.75], bah['cblack123'/23, l='MpServer', x=-54.17, y=64.00, z=-26.88], bah['lolmonster8642'/43, l='MpServer', x=29.72, y=65.00, z=37.77], bah['Holmtraskare'/22, l='MpServer', x=-28.31, y=68.56, z=-15.56], bah['pizzapeng26'/18, l='MpServer', x=-2.56, y=64.00, z=53.84], bah['timmagamar'/20, l='MpServer', x=17.41, y=65.00, z=-54.50], bah['awesomekidd28'/16, l='MpServer', x=49.42, y=66.00, z=37.67], bah['ganhura'/19, l='MpServer', x=-1.84, y=65.00, z=54.09], bah['cooly333'/14, l='MpServer', x=26.31, y=69.22, z=3.44], bah['webkinzrocks'/17, l='MpServer', x=3.82, y=65.02, z=17.95], bah['Denero_HD'/12, l='MpServer', x=-10.09, y=66.00, z=51.03], bah['chrissyboy16'/11, l='MpServer', x=55.43, y=66.00, z=34.56], bah['xZaaap'/49, l='MpServer', x=-44.10, y=85.02, z=34.21], bah['harryr75'/10, l='MpServer', x=11.73, y=64.27, z=-54.63], bah['CaptainDiscord'/8, l='MpServer', x=30.03, y=104.00, z=3.41], bah['gabthepro'/7, l='MpServer', x=-24.41, y=54.00, z=16.45], bah['rango136'/6, l='MpServer', x=-11.07, y=64.00, z=-52.96], bah['filmac'/5, l='MpServer', x=-9.09, y=65.47, z=52.59], ays['nyihockeygirl'/70, l='MpServer', x=-7.08, y=67.64, z=-20.88], mg['Painting'/155, l='MpServer', x=26.00, y=87.00, z=8.94], mg['Painting'/156, l='MpServer', x=28.94, y=87.00, z=6.00], bah['BroProMaster'/106, l='MpServer', x=58.66, y=72.05, z=17.55], mg['Painting'/154, l='MpServer', x=23.06, y=87.00, z=6.00], bah['xZaaap'/49, l='MpServer', x=-44.10, y=85.02, z=34.21], bah['Bossguy987'/108, l='MpServer', x=26.17, y=69.47, z=3.76], bah['u_uFishdu_u'/39, l='MpServer', x=47.53, y=65.98, z=36.85], bah['lolmonster8642'/43, l='MpServer', x=29.72, y=65.00, z=37.77], bah['Bossguy987'/108, l='MpServer', x=26.17, y=69.47, z=3.76], bah['BroProMaster'/106, l='MpServer', x=58.66, y=72.05, z=17.55]]
Retry entities: 0 total; []
Stacktrace:
at ayp.a(SourceFile:281)
at net.minecraft.client.Minecraft.b(SourceFile:1871)
at net.minecraft.client.Minecraft.run(SourceFile:548)
at java.lang.Thread.run(Unknown Source)

– System Details –
Details:
Minecraft Version: 1.4.6
Operating System: Windows 8 (amd64) version 6.2
Java Version: 1.7.0_10, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 426761120 bytes (406 MB) / 487915520 bytes (465 MB) up to 954466304 bytes (910 MB)
JVM Flags: 2 total; -Xms512m -Xmx1024m
AABB Pool Size: 320 (17920 bytes; 0 MB) allocated, 134 (7504 bytes; 0 MB) used
Suspicious classes: IWrUpdater, Config, WrUpdates, ...]
IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 63
ModLoader: Mods loaded: 1
ModLoader 1.4.6

LWJGL: 2.4.2
OpenGL: GeForce GTX 560/PCIe/SSE2 GL version 4.2.0, NVIDIA Corporation
Is Modded: Very likely; Jar signature invalidated
Type: Client (map_client.txt)
Texture Pack: Default
Profiler Position: N/A (disabled)
Vec3 Pool Size: 1463 (81928 bytes; 0 MB) allocated, 75 (4200 bytes; 0 MB) used

java.lang.ClassCastException: aky cannot be cast to ajk
at bdo.a(SourceFile:38)
at bdo.a(SourceFile:13)
at bdw.a(SourceFile:103)
at bdw.a(SourceFile:96)
at bav.a(RenderGlobal.java:476)
at ban.a(EntityRenderer.java:1566)
at ban.b(EntityRenderer.java:1087)
at net.minecraft.client.Minecraft.J(SourceFile:605)
at net.minecraft.client.Minecraft.run(SourceFile:534)
at java.lang.Thread.run(Unknown Source)
— END ERROR REPORT 1e2f47e3 ----------