Crash

I was in one of my worlds, it started to lag really bad i closed out and it won't let me in the world i was in but it well let me in the others.

Crash report;---- Minecraft Crash Report ----
// There are four lights!

Time: 7/10/13 10:15 AM
Description: Sending packet

java.lang.NullPointerException
	at cm.b(SourceFile:116)
	at cm.a(SourceFile:41)
	at jz.b(SourceFile:421)
	at hm.b(SourceFile:648)
	at hm.a(SourceFile:82)
	at bkz.b(SourceFile:73)
	at net.minecraft.server.MinecraftServer.t(SourceFile:488)
	at net.minecraft.server.MinecraftServer.s(SourceFile:405)
	at bkw.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:339)
	at hh.run(SourceFile:582)


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

-- Head --
Stacktrace:
	at cm.b(SourceFile:116)
	at cm.a(SourceFile:41)

-- Packet being sent --
Details:
	Packet ID: 4
	Packet class: fw
Stacktrace:
	at jz.b(SourceFile:421)
	at hm.b(SourceFile:648)
	at hm.a(SourceFile:82)
	at bkz.b(SourceFile:73)
	at net.minecraft.server.MinecraftServer.t(SourceFile:488)
	at net.minecraft.server.MinecraftServer.s(SourceFile:405)
	at bkw.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:339)
	at hh.run(SourceFile:582)

-- System Details --
Details:
	Minecraft Version: 1.6.2
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0_10, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 135864856 bytes (129 MB) / 954466304 bytes (910 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 201425 (11279800 bytes; 10 MB) allocated, 201425 (11279800 bytes; 10 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 1, tallocated: 63
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 22330 (1250480 bytes; 1 MB) allocated, 22330 (1250480 bytes; 1 MB) used
	Player Count: 0 / 8; []
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.