This is the crash report,

Time: 8/1/13 2:08 PM
Description: Ticking player

java.lang.IllegalArgumentException: Modifier name cannot be empty
at org.apache.commons.lang3.Validate.notEmpty(Validate.java:398)
at os.<init>(SourceFile:31)
at to.a(SourceFile:94)
at yd.D(SourceFile:580)
at oe.l_(SourceFile:1170)
at ue.l_(SourceFile:203)
at ju.h(SourceFile:180)
at jz.a(SourceFile:190)
at et.a(SourceFile:136)
at cm.b(SourceFile:64)
at jz.e(SourceFile:60)
at kc.b(SourceFile:37)
at bkz.b(SourceFile:84)
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 org.apache.commons.lang3.Validate.notEmpty(Validate.java:398)
at os.<init>(SourceFile:31)
at to.a(SourceFile:94)
at yd.D(SourceFile:580)
at oe.l_(SourceFile:1170)
at ue.l_(SourceFile:203)

– Player being ticked –
Details:
Entity Type: null (ju)
Entity ID: 1769975
Entity Name: leeeeeevi1
Entity's Exact location: 825.24, 53.25, -212.11
Entity's Block location: World: (825,53,-213), Chunk: (at 9,3,11 in 51,-14; contains blocks 816,0,-224 to 831,255,-209), Region: (1,-1; contains chunks 32,-32 to 63,-1, blocks 512,0,-512 to 1023,255,-1)
Entity's Momentum: 0.00, 0.00, 0.00
Stacktrace:
at ju.h(SourceFile:180)
at jz.a(SourceFile:190)
at et.a(SourceFile:136)
at cm.b(SourceFile:64)
at jz.e(SourceFile:60)

– Ticking connection –
Details:
Connection: jz@1ce43b
Stacktrace:
at kc.b(SourceFile:37)
at bkz.b(SourceFile:84)
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 (x86) version 6.1
Java Version: 1.7.0_21, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
Memory: 210443144 bytes (200 MB) / 518979584 bytes (494 MB) up to 518979584 bytes (494 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
AABB Pool Size: 299 (16744 bytes; 0 MB) allocated, 40 (2240 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: 24 (1344 bytes; 0 MB) allocated, 7 (392 bytes; 0 MB) used
Player Count: 1 / 8; [ju['leeeeeevi1'/1769975, l='Race For Wool V1.0', x=825.24, y=53.25, z=-212.11]]
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.