Crashes on Flatworld Customization

When creating a world, it crashes when you try to customize a flatworld

---- Minecraft Crash Report ----
// Oops.

Time: 7/9/13 9:10 PM
Description: Rendering screen

java.lang.IncompatibleClassChangeError: Expected non-static field auw.n
	at aux.b(SourceFile:164)
	at aux.e(SourceFile:151)
	at aux.a(SourceFile:137)
	at aux.a(SourceFile:198)
	at awd.a(SourceFile:274)
	at auw.a(GuiCreateFlatWorld.java:103)
	at bfb.b(EntityRenderer.java:1000)
	at ats.S(Minecraft.java:813)
	at ats.d(Minecraft.java:707)
	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 aux.b(SourceFile:164)
	at aux.e(SourceFile:151)
	at aux.a(SourceFile:137)
	at aux.a(SourceFile:198)
	at awd.a(SourceFile:274)
	at auw.a(GuiCreateFlatWorld.java:103)

-- Screen render details --
Details:
	Screen name: auw
	Mouse location: Scaled: (282, 136). Absolute: (565, 206)
	Screen size: Scaled: (427, 240). Absolute: (854, 480). Scale factor of 2
Stacktrace:
	at bfb.b(EntityRenderer.java:1000)
	at ats.S(Minecraft.java:813)
	at ats.d(Minecraft.java:707)
	at net.minecraft.client.main.Main.main(SourceFile:101)

-- System Details --
Details:
	Minecraft Version: 1.6.2
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 124532200 bytes (118 MB) / 171311104 bytes (163 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	Suspicious classes: KeyHack, hacks, MCGui]
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Launched Version: Rubix
	LWJGL: 2.9.0
	OpenGL: Intel(R) HD Graphics 4000 GL version 3.3.0 - Build 8.15.10.2653, Intel
	Is Modded: Very likely; Jar signature invalidated
	Type: Client (map_client.txt)
	Resource Pack: SpacePIG16_RP.zip
	Current Language: English (US)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: ~~ERROR~~ NullPointerException: null