I am running mcpc-plus-1.4.7-R1.1-SNAPSHOT-f524-188 with Forge 6.6.something.
I have absolutely no Idea what threw this as the server was only up for a few minuets.
I was the only user. This exception did not hinder mod activity at all.

18:25:28 [SEVERE] org.apache.commons.lang.UnhandledException: Plugin Essentials
v2.10.1 generated an exception while executing task 42
at org.bukkit.craftbukkit.v1_4_R1.scheduler.CraftAsyncTask.run(CraftAsyn
cTask.java:56)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
at uk.org.whoami.authme.filter.ConsoleFilter.isLoggable(Unknown Source)
at java.util.logging.Logger.log(Unknown Source)
at java.util.logging.Logger.doLog(Unknown Source)
at java.util.logging.Logger.log(Unknown Source)
at com.earth2me.essentials.Backup$1.run(Unknown Source)
at org.bukkit.craftbukkit.v1_4_R1.scheduler.CraftTask.run(CraftTask.java
:53)
at org.bukkit.craftbukkit.v1_4_R1.scheduler.CraftAsyncTask.run(CraftAsyn
cTask.java:53)
... 3 more

Not an EE3 bug - looks like something to do with a bukkit plugin called Plugin Essentials.

Sorry, I'm not much more help than that.