I have been playing in a flat map, created in mc 1.8PR for several weeks, today when I was placing/destroying wooden slabs in Creative mode the game freezed up and after some time came up with that error...
since then I am not able to play the map as I get a crash with that error everytime I load into the map...

---- Minecraft Crash Report ----
// Surprise! Haha. Well, this is awkward.

Time: 16.11.2014 15:01
Description: Tesselating block model

java.lang.ArrayIndexOutOfBoundsException: 36
at com.prupe.mcpatcher.ctm.TileOverrideImpl$CTM.getTileWorld_Impl(TileOverrideImpl.java:66)
at com.prupe.mcpatcher.ctm.TileOverride.getTileWorld(TileOverride.java:433)
at com.prupe.mcpatcher.ctm.TileOverrideIterator$IJK.getTile(TileOverrideIterator.java:146)
at com.prupe.mcpatcher.ctm.TileOverrideIterator.go(TileOverrideIterator.java:119)
at com.prupe.mcpatcher.ctm.CTMUtils18.getModelFace(CTMUtils18.java:202)
at cln.a(SourceFile:134)
at cln.a(SourceFile:74)
at cln.a(SourceFile:43)
at cln.a(SourceFile:35)
at cll.a(SourceFile:62)
at cop.b(SourceFile:154)
at coh.a(SourceFile:78)
at coh.run(SourceFile:38)
at java.lang.Thread.run(Thread.java:744)

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

– Head –
Stacktrace:
at com.prupe.mcpatcher.ctm.TileOverrideImpl$CTM.getTileWorld_Impl(TileOverrideImpl.java:66)
at com.prupe.mcpatcher.ctm.TileOverride.getTileWorld(TileOverride.java:433)
at com.prupe.mcpatcher.ctm.TileOverrideIterator$IJK.getTile(TileOverrideIterator.java:146)
at com.prupe.mcpatcher.ctm.TileOverrideIterator.go(TileOverrideIterator.java:119)
at com.prupe.mcpatcher.ctm.CTMUtils18.getModelFace(CTMUtils18.java:202)
at cln.a(SourceFile:134)
at cln.a(SourceFile:74)

– Block model being tesselated –
Details:
Block: minecraft:double_wooden_slab[variant=birch]
Block location: World: (633,56,-321), Chunk: (at 9,3,15 in 39,-21; contains blocks 624,0,-336 to 639,255,-321), Region: (1,-1; contains chunks 32,-32 to 63,-1, blocks 512,0,-512 to 1023,255,-1)
Using AO: true
Stacktrace:
at cln.a(SourceFile:43)
at cln.a(SourceFile:35)

– Block being tesselated –
Details:
Block type: ID #125 (tile.woodSlab // awi)
Block data value: 2 / 0x2 / 0b0010
Block location: World: (633,56,-321), Chunk: (at 9,3,15 in 39,-21; contains blocks 624,0,-336 to 639,255,-321), Region: (1,-1; contains chunks 32,-32 to 63,-1, blocks 512,0,-512 to 1023,255,-1)
Stacktrace:
at cll.a(SourceFile:62)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [cio['babbajagga'/17748, l='MpServer', x=635,20, y=58,12, z=-322,03]]
Chunk stats: MultiplayerChunkCache: 49, 49
Level seed: 0
Level generator: ID 01 - flat, ver 0. Features enabled: false
Level generator options:
Level spawn location: 601,00,4,00,-240,00 - World: (601,4,-240), Chunk: (at 9,0,0 in 37,-15; contains blocks 592,0,-240 to 607,255,-225), Region: (1,-1; contains chunks 32,-32 to 63,-1, blocks 512,0,-512 to 1023,255,-1)
Level time: 653485 game time, 6598 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: 1 total; [cio['babbajagga'/17748, l='MpServer', x=635,20, y=58,12, z=-322,03]]
Retry entities: 0 total; []
Server brand: vanilla
Server type: Integrated singleplayer server
Stacktrace:
at cen.a(SourceFile:308)
at bsu.b(SourceFile:2252)
at coh.run(SourceFile:44)
at java.lang.Thread.run(Thread.java:744)

– System Details –
Details:
Minecraft Version: 1.8
Operating System: Windows XP (x86) version 5.1
Java Version: 1.7.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
Memory: 376662808 bytes (359 MB) / 607727616 bytes (579 MB) up to 1060372480 bytes (1011 MB)
JVM Flags: 6 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Launched Version: 1.8-mcpatcher
LWJGL: 2.9.1
OpenGL: ~_ERROR~ RuntimeException: No OpenGL context found in the current thread.
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.
VBOs are available because OpenGL 1.5 is supported.

Using VBOs: No
Is Modded: Very likely; Jar signature invalidated
Type: Client (map_client.txt)
Resource Packs: [W.I.P. Ornate 5 RR [mc1.8+]]
Current Language: English (US)
Profiler Position: N/A (disabled)