Minecraft crashes after few minutes

---- Minecraft Crash Report ----
// You're mean.

Time: 5/8/13 2:10 PM
Description: Updating screen events

java.lang.NullPointerException
	at awp.a(SourceFile:47)
	at axr.a(SourceFile:72)
	at axr.d(SourceFile:127)
	at axr.m(SourceFile:111)
	at net.minecraft.client.Minecraft.l(SourceFile:1078)
	at net.minecraft.client.Minecraft.K(SourceFile:574)
	at net.minecraft.client.Minecraft.run(SourceFile:526)
	at java.lang.Thread.run(Unknown Source)


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

-- Head --
Stacktrace:
	at awp.a(SourceFile:47)
	at axr.a(SourceFile:72)
	at axr.d(SourceFile:127)
	at axr.m(SourceFile:111)

-- Affected screen --
Details:
	Screen name: bkf
Stacktrace:
	at net.minecraft.client.Minecraft.l(SourceFile:1078)
	at net.minecraft.client.Minecraft.K(SourceFile:574)
	at net.minecraft.client.Minecraft.run(SourceFile:526)
	at java.lang.Thread.run(Unknown Source)

-- System Details --
Details:
	Minecraft Version: 1.5.2
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_21, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
	Memory: 368252832 bytes (351 MB) / 519110656 bytes (495 MB) up to 1037959168 bytes (989 MB)
	JVM Flags: 2 total; -Xms512m -Xmx1024m
	AABB Pool Size: 79911 (4475016 bytes; 4 MB) allocated, 2 (112 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 4, tallocated: 68
	LWJGL: 2.4.2
	OpenGL: Intel(R) HD Graphics GL version 2.1.0 - Build 8.15.10.2119, Intel
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Texture Pack: Default
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: ~~ERROR~~ NullPointerException: null