crash on launch after dying in portal

Died in a portal, now I get this when I try to load my world.

Minecraft has crashed!
----------------------

Minecraft has stopped running because it encountered a problem; Exception in server tick loop

A full error report has been saved to /home/drink/.minecraft/crash-reports/crash-2013-04-19_08.14.51-server.txt - Please include a copy of that file (Not this screen!) if you report this crash to anyone; without it, they will not be able to help fix the crash

— BEGIN ERROR REPORT a7803136 --------
Full report at:
/home/drink/.minecraft/crash-reports/crash-2013-04-19_08.14.51-server.txt
Please show that file to Mojang, NOT just this screen!

Generated 4/19/13 8:15 AM

– System Details –
Details:
Minecraft Version: 1.5.1
Operating System: Linux (amd64) version 3.5.0-27-generic
Java Version: 1.7.0_15, Oracle Corporation
Java VM Version: OpenJDK 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 301524128 bytes (287 MB) / 557449216 bytes (531 MB) up to 1862270976 bytes (1776 MB)
JVM Flags: 0 total;
AABB Pool Size: 2883 (161448 bytes; 0 MB) allocated, 2883 (161448 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: 731 (40936 bytes; 0 MB) allocated, 731 (40936 bytes; 0 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.

java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:894)
at java.util.HashMap$KeyIterator.next(HashMap.java:928)
at it.a(SourceFile:126)
at net.minecraft.server.MinecraftServer.r(SourceFile:470)
at net.minecraft.server.MinecraftServer.q(SourceFile:397)
at bjh.q(SourceFile:122)
at net.minecraft.server.MinecraftServer.run(SourceFile:331)
at gp.run(SourceFile:573)
— END ERROR REPORT ebcf06f6 ----------