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-83831/

Crash:

java.lang.RuntimeException: Failed to check session lock, aborting
	at anq.h(SourceFile:44)
	at anq.<init>(SourceFile:30)
	at anm.<init>(SourceFile:16)
	at ann.a(SourceFile:68)
	at awb.a(SourceFile:1463)
	at axy.a(SourceFile:202)
	at ayw.a(SourceFile:71)
	at axy.a(SourceFile:301)
	at ayw.d(SourceFile:139)
	at ayw.m(SourceFile:110)

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

---- Minecraft Crash Report ----
// Don't be sad. I'll do better next time, I promise!

Time: 09/06/13 03:35 PM
Description: Updating screen events

java.lang.RuntimeException: Failed to check session lock, aborting
	at anq.h(SourceFile:44)
	at anq.<init>(SourceFile:30)
	at anm.<init>(SourceFile:16)
	at ann.a(SourceFile:68)
	at awb.a(SourceFile:1463)
	at axy.a(SourceFile:202)
	at ayw.a(SourceFile:71)
	at axy.a(SourceFile:301)
	at ayw.d(SourceFile:139)
	at ayw.m(SourceFile:110)
	at awb.m(SourceFile:1202)
	at awb.V(SourceFile:686)
	at awb.e(SourceFile:642)
	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 anq.h(SourceFile:44)
	at anq.<init>(SourceFile:30)
	at anm.<init>(SourceFile:16)
	at ann.a(SourceFile:68)
	at awb.a(SourceFile:1463)
	at axy.a(SourceFile:202)
	at ayw.a(SourceFile:71)
	at axy.a(SourceFile:301)
	at ayw.d(SourceFile:139)
	at ayw.m(SourceFile:110)

-- Affected screen --
Details:
	Screen name: bof
Stacktrace:
	at awb.m(SourceFile:1202)
	at awb.V(SourceFile:686)
	at awb.e(SourceFile:642)
	at net.minecraft.client.main.Main.main(SourceFile:103)

-- System Details --
Details:
	Minecraft Version: 13w36b
	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: 41450960 bytes (39 MB) / 70971392 bytes (67 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 1 total; -Xmx512M
	AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Launched Version: 13w36b
	LWJGL: 2.9.0
	OpenGL: Intel(R) HD Graphics Family GL version 3.0.0 - Build 8.15.10.2291, Intel
	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

You can see this full report at http://hopper.minecraft.net/crashes/minecraft/MCX-83831/8415777/