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-468498/

Crash:

java.lang.RuntimeException: Failed to check session lock, aborting
	at axc.h(SourceFile:48)
	at axc.<init>(SourceFile:34)
	at awy.<init>(SourceFile:16)
	at awz.a(SourceFile:71)
	at azd.a(SourceFile:1578)
	at btj.a(SourceFile:277)
	at bcd.a(SourceFile:172)
	at btj.a(SourceFile:517)
	at bcd.d(SourceFile:236)
	at bcd.k(SourceFile:211)

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

---- Minecraft Crash Report ----
// Uh... Did I do that?

Time: 25.10.2013 22:51
Description: Updating screen events

java.lang.RuntimeException: Failed to check session lock, aborting
	at axc.h(SourceFile:48)
	at axc.<init>(SourceFile:34)
	at awy.<init>(SourceFile:16)
	at awz.a(SourceFile:71)
	at azd.a(SourceFile:1578)
	at btj.a(SourceFile:277)
	at bcd.a(SourceFile:172)
	at btj.a(SourceFile:517)
	at bcd.d(SourceFile:236)
	at bcd.k(SourceFile:211)
	at azd.o(SourceFile:1303)
	at azd.ad(SourceFile:753)
	at azd.e(SourceFile:704)
	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:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
	at axc.h(SourceFile:48)
	at axc.<init>(SourceFile:34)
	at awy.<init>(SourceFile:16)
	at awz.a(SourceFile:71)
	at azd.a(SourceFile:1578)
	at btj.a(SourceFile:277)
	at bcd.a(SourceFile:172)
	at btj.a(SourceFile:517)
	at bcd.d(SourceFile:236)
	at bcd.k(SourceFile:211)

-- Affected screen --
Details:
	Screen name: btj
Stacktrace:
	at azd.o(SourceFile:1303)
	at azd.ad(SourceFile:753)
	at azd.e(SourceFile:704)
	at net.minecraft.client.main.Main.main(SourceFile:103)

-- System Details --
Details:
	Minecraft Version: 1.7.2
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_45, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 109633496 bytes (104 MB) / 189468672 bytes (180 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: 1.7.2
	LWJGL: 2.9.0
	OpenGL: ATI Mobility Radeon HD 2400 GL version 3.3.11672 Compatibility Profile Context, ATI Technologies Inc.
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Packs: []
	Current Language: English (US)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: ~~ERROR~~ NullPointerException: null
	Anisotropic Filtering: Off (1)

You can see this full report at http://hopper.minecraft.net/crashes/minecraft/MCX-468498/21478708/