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-450040/

Crash:

java.lang.RuntimeException: Failed to check session lock, aborting
	at axb.h(SourceFile:48)
	at axb.<init>(SourceFile:34)
	at awx.<init>(SourceFile:16)
	at awy.a(SourceFile:71)
	at azc.a(SourceFile:1578)
	at bbh.a(SourceFile:202)
	at bcc.a(SourceFile:172)
	at bbh.a(SourceFile:301)
	at bcc.d(SourceFile:236)
	at bcc.k(SourceFile:211)

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

---- Minecraft Crash Report ----
// Would you like a cupcake?

Time: 10/23/13 5:05 PM
Description: Updating screen events

java.lang.RuntimeException: Failed to check session lock, aborting
	at axb.h(SourceFile:48)
	at axb.<init>(SourceFile:34)
	at awx.<init>(SourceFile:16)
	at awy.a(SourceFile:71)
	at azc.a(SourceFile:1578)
	at bbh.a(SourceFile:202)
	at bcc.a(SourceFile:172)
	at bbh.a(SourceFile:301)
	at bcc.d(SourceFile:236)
	at bcc.k(SourceFile:211)
	at azc.o(SourceFile:1303)
	at azc.ad(SourceFile:753)
	at azc.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 axb.h(SourceFile:48)
	at axb.<init>(SourceFile:34)
	at awx.<init>(SourceFile:16)
	at awy.a(SourceFile:71)
	at azc.a(SourceFile:1578)
	at bbh.a(SourceFile:202)
	at bcc.a(SourceFile:172)
	at bbh.a(SourceFile:301)
	at bcc.d(SourceFile:236)
	at bcc.k(SourceFile:211)

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

-- System Details --
Details:
	Minecraft Version: 1.7.1
	Operating System: Mac OS X (x86_64) version 10.7.5
	Java Version: 1.6.0_51, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 67691952 bytes (64 MB) / 107892736 bytes (102 MB) up to 1069416448 bytes (1019 MB)
	JVM Flags: 1 total; -Xmx1G
	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: 1.7.1
	LWJGL: 2.9.1
	OpenGL: ATI Radeon HD 4670 OpenGL Engine GL version 2.1 ATI-7.32.12, 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 (UK)
	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-450040/20955713/