Bukkit

I was checking my server logs this morning and I found the following error:
2013-06-13 04:34:51 [SEVERE] Exception in thread "pool-1-thread-2737"
2013-06-13 04:34:51 [SEVERE] org.apache.commons.lang.UnhandledException: Plugin AlwaysDay v2.2.7 generated an exception while executing task 29
    at org.bukkit.craftbukkit.v1_5_R3.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:722)
Caused by: java.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:819)
    at java.util.ArrayList$Itr.next(ArrayList.java:791)
    at org.bukkit.craftbukkit.v1_5_R3.CraftWorld.getPlayers(CraftWorld.java:630)
    at org.bukkit.craftbukkit.v1_5_R3.CraftWorld.setFullTime(CraftWorld.java:442)
    at org.bukkit.craftbukkit.v1_5_R3.CraftWorld.setTime(CraftWorld.java:431)
    at me.LlamaGoingNorth.alwaysday.AlwaysDay$1.run(AlwaysDay.java:329)
    at org.bukkit.craftbukkit.v1_5_R3.scheduler.CraftTask.run(CraftTask.java:53)
    at org.bukkit.craftbukkit.v1_5_R3.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
    ... 3 more

The only other thing I saw was my memory usage was over 5.5GB for some reason and I do not know if this was the cause of the leak.

Has this occurred again or was this a one off?

This is an error caused by the bukkit server (it failed to get the players), which meant that AlwaysDay couldn't control the time cycles. This is not due to AlwaysDay.