[06:50:11] [Server thread/ERROR] [FML]: Exception caught during firing event cpw.mods.fml.common.gameevent.TickEvent$ServerTickEvent@66d0f168:
java.util.ConcurrentModificationException
    at java.util.HashMap$HashIterator.remove(HashMap.java:940) ~[?:1.7.0_65]
    at net.doubledoordev.pay2spawn.util.CountdownTickHandler.tickEvent(CountdownTickHandler.java:104) ~[CountdownTickHandler.class:?]
    at cpw.mods.fml.common.eventhandler.ASMEventHandler_405_CountdownTickHandler_tickEvent_TickEvent.invoke(.dynamic) ~[?:?]
    at cpw.mods.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:54) ~[ASMEventHandler.class:?]
    at cpw.mods.fml.common.eventhandler.EventBus.post(EventBus.java:138) [EventBus.class:?]
    at cpw.mods.fml.common.FMLCommonHandler.onPreServerTick(FMLCommonHandler.java:260) [FMLCommonHandler.class:?]
    at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:536) [MinecraftServer.class:?]
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:427) [MinecraftServer.class:?]
    at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685) [li.class:?]