Boos Error

2012-02-06 17:12:38 [WARNING] Task of 'boosCooldown' generated an exception
java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextEntry(HashMap.java:839)
	at java.util.HashMap$KeyIterator.next(HashMap.java:874)
	at cz.boosik.boosCooldown.boosCoolDownPlayerListener.clearLocWorld(boosCoolDownPlayerListener.java:240)
	at cz.boosik.boosCooldown.boosWarmUpTimer$boosWarmUpRunnable.run(boosWarmUpTimer.java:36)
	at org.bukkit.craftbukkit.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:137)
	at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:503)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:435)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:465)