09:03:41 [SEVERE] null
org.bukkit.command.CommandException: Unhandled exception executing command 'hero
strong' in plugin HeroStronghold v0.1
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:42)
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:16
5)
        at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:3
78)
        at net.minecraft.server.NetServerHandler.handleCommand(NetServerHandler.
java:756)
        at net.minecraft.server.NetServerHandler.chat(NetServerHandler.java:721)

        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:714)
        at net.minecraft.server.Packet3Chat.a(Packet3Chat.java:33)
        at net.minecraft.server.NetworkManager.b(NetworkManager.java:226)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:92)
        at net.minecraft.server.NetworkListenThread.a(SourceFile:108)
        at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:527)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:425)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:457)
Caused by: java.util.ConcurrentModificationException
        at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
        at java.util.ArrayList$Itr.next(Unknown Source)
        at main.java.multitallented.plugins.herostronghold.HeroStronghold.onComm
and(HeroStronghold.java:118)
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:40)
        ... 12 more