Hopper: java.lang.RuntimeException: Failed to check session lock, aborting

This is an automatically generated report based from the following crash: http://hopper.minecraft.net/crashes/minecraft/MCX-191552/

Crash:

java.lang.RuntimeException: Failed to check session lock, aborting
	at alq.h(SourceFile:44)
	at alq.<init>(SourceFile:30)
	at alm.<init>(SourceFile:16)
	at aln.a(SourceFile:83)
	at atv.a(SourceFile:1417)
	at awh.e(SourceFile:157)
	at awh.a(SourceFile:122)
	at awe.a(SourceFile:69)
	at awe.d(SourceFile:128)
	at awe.m(SourceFile:107)

The following is the first clean report made public about this crash:

---- Minecraft Crash Report ----
// There are four lights!

Time: 9/19/13 3:55 PM
Description: Updating screen events

java.lang.RuntimeException: Failed to check session lock, aborting
	at alq.h(SourceFile:44)
	at alq.<init>(SourceFile:30)
	at alm.<init>(SourceFile:16)
	at aln.a(SourceFile:83)
	at atv.a(SourceFile:1417)
	at awh.e(SourceFile:157)
	at awh.a(SourceFile:122)
	at awe.a(SourceFile:69)
	at awe.d(SourceFile:128)
	at awe.m(SourceFile:107)
	at atv.k(SourceFile:1158)
	at atv.S(SourceFile:663)
	at atv.d(SourceFile:619)
	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 alq.h(SourceFile:44)
	at alq.<init>(SourceFile:30)
	at alm.<init>(SourceFile:16)
	at aln.a(SourceFile:83)
	at atv.a(SourceFile:1417)
	at awh.e(SourceFile:157)
	at awh.a(SourceFile:122)
	at awe.a(SourceFile:69)
	at awe.d(SourceFile:128)
	at awe.m(SourceFile:107)

-- Affected screen --
Details:
	Screen name: blt
Stacktrace:
	at atv.k(SourceFile:1158)
	at atv.S(SourceFile:663)
	at atv.d(SourceFile:619)
	at net.minecraft.client.main.Main.main(SourceFile:101)

-- System Details --
Details:
	Minecraft Version: 1.6.4
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 41246864 bytes (39 MB) / 70639616 bytes (67 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
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Launched Version: 1.6.4
	LWJGL: 2.9.0
	OpenGL: Intel 945GM GL version 1.4.0 - Build 8.14.10.1930, Intel
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Pack: Default
	Current Language: English (US)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: ~~ERROR~~ NullPointerException: null

You can see this full report at http://hopper.minecraft.net/crashes/minecraft/MCX-191552/12425257/