Crash when creating new world

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

Time: 7-7-13 22:29
Description: Updating screen events

java.lang.RuntimeException: Failed to check session lock, aborting
	at alj.h(SourceFile:44)
	at alj.<init>(SourceFile:30)
	at alf.<init>(SourceFile:16)
	at alg.a(SourceFile:83)
	at atn.a(SourceFile:1411)
	at aus.a(SourceFile:202)
	at avv.a(SourceFile:71)
	at aus.a(SourceFile:302)
	at avv.d(SourceFile:125)
	at avv.m(SourceFile:109)
	at atn.k(SourceFile:1157)
	at atn.S(SourceFile:662)
	at atn.d(SourceFile:618)
	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 alj.h(SourceFile:44)
	at alj.<init>(SourceFile:30)
	at alf.<init>(SourceFile:16)
	at alg.a(SourceFile:83)
	at atn.a(SourceFile:1411)
	at aus.a(SourceFile:202)
	at avv.a(SourceFile:71)
	at aus.a(SourceFile:302)
	at avv.d(SourceFile:125)
	at avv.m(SourceFile:109)

-- Affected screen --
Details:
	Screen name: bli
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 7 (amd64) version 6.1
	Java Version: 1.7.0_09, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 217020872 bytes (206 MB) / 250347520 bytes (238 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: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Launched Version: 1.6.1
	LWJGL: 2.9.0
	OpenGL: GeForce GTX 660 Ti/PCIe/SSE2 GL version 4.3.0, NVIDIA Corporation
	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

Duplicate of MC-10167, please use the search function to see if your bug has already been submitted. Currently over 58% of tickets are being closed as duplicate.