RPGDrops Error

2012-09-24 14:07:31 [SEVERE] Could not pass event EntityDeathEvent to RPGDrop
org.bukkit.event.EventException
	at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:332)
	at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
	at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:477)
	at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:462)
	at org.bukkit.craftbukkit.event.CraftEventFactory.callEntityDeathEvent(CraftEventFactory.java:299)
	at net.minecraft.server.EntityCow.dropDeathLoot(EntityCow.java:70)
	at net.minecraft.server.EntityLiving.die(EntityLiving.java:767)
	at net.minecraft.server.EntityLiving.damageEntity(EntityLiving.java:663)
	at net.minecraft.server.EntityAnimal.damageEntity(SourceFile:124)
	at net.minecraft.server.EntityHuman.attack(EntityHuman.java:762)
	at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:1019)
	at me.blablubbabc.insigns.NetServerHandlerInstance.a(NetServerHandlerInstance.java:143)
	at net.minecraft.server.Packet7UseEntity.handle(SourceFile:36)
	at net.minecraft.server.NetworkManager.b(NetworkManager.java:276)
	at net.minecraft.server.NetServerHandler.d(NetServerHandler.java:109)
	at net.minecraft.server.ServerConnection.b(SourceFile:35)
	at net.minecraft.server.DedicatedServerConnection.b(SourceFile:30)
	at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:578)
	at net.minecraft.server.DedicatedServer.q(DedicatedServer.java:213)
	at net.minecraft.server.MinecraftServer.p(MinecraftServer.java:474)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:406)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:539)
Caused by: java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
	at java.util.ArrayList$Itr.next(Unknown Source)
	at me.ceoepts.RD.RDListener.Drop(RDListener.java:26)
	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:330)
	... 21 more