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-197728/

Crash:

java.lang.RuntimeException: Failed to check session lock, aborting
	at aod.h(SourceFile:45)
	at aod.<init>(SourceFile:31)
	at anz.<init>(SourceFile:16)
	at aoa.a(SourceFile:68)
	at awp.a(SourceFile:1522)
	at ays.a(SourceFile:202)
	at azq.a(SourceFile:172)
	at ays.a(SourceFile:301)
	at azq.d(SourceFile:236)
	at azq.m(SourceFile:211)

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

---- Minecraft Crash Report ----
// Why did you do that?

Time: 9/20/13 4:40 PM
Description: Updating screen events

java.lang.RuntimeException: Failed to check session lock, aborting
	at aod.h(SourceFile:45)
	at aod.<init>(SourceFile:31)
	at anz.<init>(SourceFile:16)
	at aoa.a(SourceFile:68)
	at awp.a(SourceFile:1522)
	at ays.a(SourceFile:202)
	at azq.a(SourceFile:172)
	at ays.a(SourceFile:301)
	at azq.d(SourceFile:236)
	at azq.m(SourceFile:211)
	at awp.o(SourceFile:1256)
	at awp.aa(SourceFile:726)
	at awp.e(SourceFile:677)
	at net.minecraft.client.main.Main.main(SourceFile:104)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
	at aod.h(SourceFile:45)
	at aod.<init>(SourceFile:31)
	at anz.<init>(SourceFile:16)
	at aoa.a(SourceFile:68)
	at awp.a(SourceFile:1522)
	at ays.a(SourceFile:202)
	at azq.a(SourceFile:172)
	at ays.a(SourceFile:301)
	at azq.d(SourceFile:236)
	at azq.m(SourceFile:211)

-- Affected screen --
Details:
	Screen name: bpl
Stacktrace:
	at awp.o(SourceFile:1256)
	at awp.aa(SourceFile:726)
	at awp.e(SourceFile:677)
	at net.minecraft.client.main.Main.main(SourceFile:104)

-- System Details --
Details:
	Minecraft Version: 13w38c
	Operating System: Mac OS X (x86_64) version 10.8.4
	Java Version: 1.6.0_51, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 62424592 bytes (59 MB) / 98254848 bytes (93 MB) up to 1065025536 bytes (1015 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: 13w38c
	LWJGL: 2.9.0
	OpenGL: AMD Radeon HD 6750M OpenGL Engine GL version 2.1 ATI-1.8.18, 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

You can see this full report at http://hopper.minecraft.net/crashes/minecraft/MCX-197728/12727741/