Need someone to look this over for me

Alright, was making an events plug-in and it will not work for me.

http://prntscr.com/prmlg

[SEVERE] Could not pass event PlayerDeathEvent to TheHidden v0.1
org.bukkit.event.EventException
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:427)
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:477)
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:462)
at org.bukkit.craftbukkit.v1_4_6.event.CraftEventFactory.callPlayerDeathEvent(CraftEventFactory.java:330)
at net.minecraft.server.v1_4_6.EntityPlayer.die(EntityPlayer.java:254)
at net.minecraft.server.v1_4_6.EntityLiving.damageEntity(EntityLiving.java:746)
at net.minecraft.server.v1_4_6.EntityHuman.damageEntity(EntityHuman.java:614)
at net.minecraft.server.v1_4_6.EntityPlayer.damageEntity(EntityPlayer.java:307)
at net.minecraft.server.v1_4_6.EntityHuman.attack(EntityHuman.java:803)
at net.minecraft.server.v1_4_6.PlayerConnection.a(PlayerConnection.java:1119)
at net.minecraft.server.v1_4_6.Packet7UseEntity.handle(SourceFile:36)
at net.minecraft.server.v1_4_6.NetworkManager.b(NetworkManager.java:290)
at net.minecraft.server.v1_4_6.PlayerConnection.d(PlayerConnection.java:112)
at net.minecraft.server.v1_4_6.ServerConnection.b(SourceFile:39)
at net.minecraft.server.v1_4_6.DedicatedServerConnection.b(SourceFile:30)
at net.minecraft.server.v1_4_6.MinecraftServer.r(MinecraftServer.java:598)
at net.minecraft.server.v1_4_6.DedicatedServer.r(DedicatedServer.java:224)
at net.minecraft.server.v1_4_6.MinecraftServer.q(MinecraftServer.java:494)
at net.minecraft.server.v1_4_6.MinecraftServer.run(MinecraftServer.java:427)
at net.minecraft.server.v1_4_6.ThreadServerApplication.run(SourceFile:849)
Caused by: java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
at java.util.ArrayList$Itr.next(Unknown Source)
at com.dystopiangaming.WafflesYumyum.Hidden.onPlayerDeath(Hidden.java:101)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:425)
... 20 more

Someone please help me...