Hopper: java.lang.ClassCastException: aqr cannot be cast to amv

This is an automatically generated report based from the following crash: http://hopper.minecraft.net/crashes/minecraft/MCX-12888/

Crash:

java.lang.ClassCastException: aqr cannot be cast to amv
	at amw.<init>(SourceFile:33)
	at amv.a(SourceFile:372)
	at amv.a(SourceFile:334)
	at adq.a(SourceFile:395)
	at abv.f(SourceFile:306)
	at aiq.a(SourceFile:384)
	at aiq.a(SourceFile:513)
	at agh.a(SourceFile:392)
	at ais.a(SourceFile:29)
	at aim.a(SourceFile:72)
	at aes.a(SourceFile:425)
	at jq.a(SourceFile:168)
	at adq.a(SourceFile:729)
	at jq.c(SourceFile:105)
	at jp.<init>(SourceFile:29)
	at jo.a(SourceFile:208)
	at jo.a(SourceFile:240)
	at hm.a(SourceFile:141)
	at hm.c(SourceFile:188)
	at hm.a(SourceFile:85)
	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)

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

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

Time: 8/4/13 3:40 PM
Description: Exception in server tick loop

java.lang.NullPointerException
	at amw.<init>(SourceFile:33)
	at amv.a(SourceFile:372)
	at amv.a(SourceFile:334)
	at adq.a(SourceFile:395)
	at abv.f(SourceFile:306)
	at aiq.a(SourceFile:384)
	at aiq.a(SourceFile:513)
	at agh.a(SourceFile:392)
	at ais.a(SourceFile:29)
	at aim.a(SourceFile:72)
	at aes.a(SourceFile:425)
	at jq.a(SourceFile:168)
	at adq.a(SourceFile:729)
	at jq.c(SourceFile:105)
	at jp.<init>(SourceFile:29)
	at jo.a(SourceFile:208)
	at jo.a(SourceFile:240)
	at hm.a(SourceFile:141)
	at hm.c(SourceFile:188)
	at hm.a(SourceFile:85)
	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:
---------------------------------------------------------------------------------------

-- System Details --
Details:
	Minecraft Version: 1.6.2
	Operating System: Windows XP (x86) version 5.1
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 13130608 bytes (12 MB) / 109285376 bytes (104 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
	AABB Pool Size: 4898 (274288 bytes; 0 MB) allocated, 4898 (274288 bytes; 0 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: 4230 (236880 bytes; 0 MB) allocated, 4230 (236880 bytes; 0 MB) used
	Player Count: 1 / 8; [ju['austin_lee_world'/393, l='vanessa', x=-149.24, y=63.00, z=272.16]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.

You can see this full report at http://hopper.minecraft.net/crashes/minecraft/MCX-12888/573638/