A detailed walkthrough of the error, its code path and all known details is as follows:
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– Head –
Stacktrace:
at java.lang.Thread.start0(Native Method)
at java.lang.Thread.start(Unknown Source)
at ave.A_(SourceFile:90)
at avv.a(SourceFile:96)
at atn.a(SourceFile:549)
at bli.a(SourceFile:259)
at avv.a(SourceFile:71)
at bli.a(SourceFile:503)
at avv.d(SourceFile:125)
at avv.m(SourceFile:109)

– Affected screen –
Details:
Screen name: ave
Stacktrace:
at atn.k(SourceFile:1157)
at atn.S(SourceFile:662)
at atn.d(SourceFile:618)
at net.minecraft.client.main.Main.main(SourceFile:101)

– System Details –
Details:
Minecraft Version: 1.6.1
Operating System: Windows 8 (x86) version 6.2
Java Version: 1.7.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
Memory: 188122864 bytes (179 MB) / 488050688 bytes (465 MB) up to 1037959168 bytes (989 MB)
JVM Flags: 1 total; -Xmx1G
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 1, tallocated: 63
Launched Version: 1.6.1
LWJGL: 2.9.0
OpenGL: Intel(R) HD Graphics GL version 3.1.0 - Build 9.17.10.2817, Intel
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Pack: Default
Profiler Position: N/A (disabled)
Vec3 Pool Size: ~_ERROR~ NullPointerException: null