Hopper: java.lang.ClassCastException: bib cannot be cast to fk

java.lang.ClassCastException: bib cannot be cast to fk
	at gs.a(SourceFile:13)
	at ek.a(SourceFile:146)
	at ayp.o(SourceFile:1561)
	at ayp.ab(SourceFile:755)
	at ayp.e(SourceFile:706)
	at net.minecraft.client.main.Main.main(SourceFile:103)

---- Minecraft Crash Report ----
// I bet Cylons wouldn't have this problem.

Time: 12.10.13 04:13
Description: Unexpected error

java.lang.ClassCastException: bib cannot be cast to fk
	at gs.a(SourceFile:13)
	at ek.a(SourceFile:146)
	at ayp.o(SourceFile:1561)
	at ayp.ab(SourceFile:755)
	at ayp.e(SourceFile:706)
	at net.minecraft.client.main.Main.main(SourceFile:103)


A detailed walkthrough of the error, its code path and all known details is as follows:
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-- System Details --
Details:
	Minecraft Version: 13w41b
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_40, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
	Memory: 32273688 bytes (30 MB) / 143265792 bytes (136 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
	AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
	Launched Version: 13w41b
	LWJGL: 2.9.0
	OpenGL: GeForce 9600 GT/PCIe/SSE2/3DNOW! GL version 3.3.0, NVIDIA Corporation
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Packs: []
	Current Language: Deutsch (Deutschland)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: ~~ERROR~~ NullPointerException: null
	Anisotropic Filtering: Off (1)