Hopper: java.lang.ClassCastException: ck cannot be cast to cj

This is an automatically generated report based from the following crash: http://hopper.minecraft.net/crashes/minecraft/MCX-304972/

Crash:

java.lang.ClassCastException: ck cannot be cast to cj
	at by.d(SourceFile:120)
	at aaw.a(SourceFile:99)
	at aaw.a(SourceFile:110)
	at aaw.a(SourceFile:137)
	at of.c(SourceFile:800)
	at uf.d(SourceFile:737)
	at of.a(SourceFile:570)
	at uf.a(SourceFile:694)
	at jv.a(SourceFile:267)
	at of.b(SourceFile:741)
	at uf.b(SourceFile:1309)
	at nn.a(SourceFile:701)
	at of.a(SourceFile:153)
	at jv.b(SourceFile:351)
	at ka.a(SourceFile:268)
	at eu.a(SourceFile:136)
	at cn.b(SourceFile:64)
	at ka.e(SourceFile:60)
	at kd.b(SourceFile:37)
	at blc.b(SourceFile:84)
	at net.minecraft.server.MinecraftServer.t(SourceFile:489)
	at net.minecraft.server.MinecraftServer.s(SourceFile:406)
	at bkz.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:340)
	at hi.run(SourceFile:583)

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

---- Minecraft Crash Report ----
// Don't be sad. I'll do better next time, I promise!

Time: 10/15/13 3:58 PM
Description: Reading NBT data

java.lang.ClassCastException: cf cannot be cast to cj
	at by.d(SourceFile:120)
	at aaw.a(SourceFile:99)
	at aaw.a(SourceFile:110)
	at aaw.a(SourceFile:137)
	at of.c(SourceFile:800)
	at uf.d(SourceFile:737)
	at of.a(SourceFile:570)
	at uf.a(SourceFile:694)
	at jv.a(SourceFile:267)
	at of.b(SourceFile:741)
	at uf.b(SourceFile:1309)
	at nn.a(SourceFile:701)
	at of.a(SourceFile:153)
	at jv.b(SourceFile:351)
	at ka.a(SourceFile:268)
	at eu.a(SourceFile:136)
	at cn.b(SourceFile:64)
	at ka.e(SourceFile:60)
	at kd.b(SourceFile:37)
	at blc.b(SourceFile:84)
	at net.minecraft.server.MinecraftServer.t(SourceFile:489)
	at net.minecraft.server.MinecraftServer.s(SourceFile:406)
	at bkz.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:340)
	at hi.run(SourceFile:583)


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

-- Corrupt NBT tag --
Details:
	Tag type found: INT
	Tag type expected: SHORT
	Tag name: id
Stacktrace:
	at by.d(SourceFile:120)
	at aaw.a(SourceFile:99)
	at aaw.a(SourceFile:110)
	at aaw.a(SourceFile:137)
	at of.c(SourceFile:800)
	at uf.d(SourceFile:737)
	at of.a(SourceFile:570)
	at uf.a(SourceFile:694)
	at jv.a(SourceFile:267)
	at of.b(SourceFile:741)
	at uf.b(SourceFile:1309)
	at nn.a(SourceFile:701)
	at of.a(SourceFile:153)
	at jv.b(SourceFile:351)
	at ka.a(SourceFile:268)
	at eu.a(SourceFile:136)
	at cn.b(SourceFile:64)
	at ka.e(SourceFile:60)

-- Ticking connection --
Details:
	Connection: ka@1ceb49a5
Stacktrace:
	at kd.b(SourceFile:37)
	at blc.b(SourceFile:84)
	at net.minecraft.server.MinecraftServer.t(SourceFile:489)
	at net.minecraft.server.MinecraftServer.s(SourceFile:406)
	at bkz.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:340)
	at hi.run(SourceFile:583)

-- System Details --
Details:
	Minecraft Version: 1.6.4
	Operating System: Mac OS X (x86_64) version 10.7.5
	Java Version: 1.6.0_45, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 52006760 bytes (49 MB) / 125136896 bytes (119 MB) up to 1065025536 bytes (1015 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 275 (15400 bytes; 0 MB) allocated, 39 (2184 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 63
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 6 (336 bytes; 0 MB) allocated, 2 (112 bytes; 0 MB) used
	Player Count: 1 / 8; [jv['Dinodude232'/45756, l='Carpet Parkour', x=-35.84, y=8.00, z=2.72]]
	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-304972/18226344/