Everytime I try to play a world, LAN, normal or online, minecraft crashes

---- Minecraft Crash Report ----
// Ooh. Shiny.

Time: 01/06/13 20:29
Description: Initializing game

javax.imageio.IIOException: Error reading PNG metadata
	at com.sun.imageio.plugins.png.PNGImageReader.readMetadata(Unknown Source)
	at com.sun.imageio.plugins.png.PNGImageReader.readImage(Unknown Source)
	at com.sun.imageio.plugins.png.PNGImageReader.read(Unknown Source)
	at javax.imageio.ImageIO.read(Unknown Source)
	at javax.imageio.ImageIO.read(Unknown Source)
	at bgv.a(SourceFile:160)
	at asx.N(SourceFile:301)
	at asx.d(SourceFile:587)
	at net.minecraft.client.main.Main.main(SourceFile:78)
Caused by: java.io.EOFException
	at javax.imageio.stream.ImageInputStreamImpl.readFully(Unknown Source)
	at java.io.DataInputStream.readUTF(Unknown Source)
	at javax.imageio.stream.ImageInputStreamImpl.readUTF(Unknown Source)
	at com.sun.imageio.plugins.png.PNGImageReader.parse_iTXt_chunk(Unknown Source)
	... 9 more


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

-- Head --
Stacktrace:
	at com.sun.imageio.plugins.png.PNGImageReader.readMetadata(Unknown Source)
	at com.sun.imageio.plugins.png.PNGImageReader.readImage(Unknown Source)
	at com.sun.imageio.plugins.png.PNGImageReader.read(Unknown Source)
	at javax.imageio.ImageIO.read(Unknown Source)
	at javax.imageio.ImageIO.read(Unknown Source)
	at bgv.a(SourceFile:160)
	at asx.N(SourceFile:301)

-- Initialization --
Details:
Stacktrace:
	at asx.d(SourceFile:587)
	at net.minecraft.client.main.Main.main(SourceFile:78)

-- System Details --
Details:
	Minecraft Version: 13w21b
	Operating System: Windows XP (x86) version 5.1
	Java Version: 1.6.0_06, Sun Microsystems Inc.
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Sun Microsystems Inc.
	Memory: 4675696 bytes (4 MB) / 46735360 bytes (44 MB) up to 1065484288 bytes (1016 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	LWJGL: 2.9.0
	OpenGL: Intel Cantiga GL version 1.5.0 - Build 7.14.10.4953, Intel
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Texture Pack: JohnSmithLegacy.zip
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: ~~ERROR~~ NullPointerException: null

This morning, it was fine, now, in the evening, it's fine, MinecraftDev crashes upon the launcher opening minecraft except on 1.5.2, which works, until i want to open the map, then, before I can see any loaded blocks, etc. it crashes! The Old Launcher does the same as 1.5.2. Why does this happen? I need help!