Exception in thread "Craft Scheduler Thread - 1147"
[16:30:44 WARN]: org.apache.commons.lang.UnhandledException: Plugin LeaderHeads v10.1.1 generated an exception while executing task 780
        at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)
Caused by: java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
        at java.util.HashMap$ValueIterator.next(HashMap.java:1458)
        at me.robin.leaderheads.N.a$5.run(SkyWarsReloadedManager.java:145)
        at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftTask.run(CraftTask.java:71)
        at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
        ... 3 more