Not sure if relevant.

15:28:59 [SEVERE] Could not pass event AsyncPlayerChatEvent to AutoReferee v2.0
org.bukkit.event.EventException
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:427)
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:477)
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:459)
at net.minecraft.server.v1_4_R1.PlayerConnection.chat(PlayerConnection.java:913)
at net.minecraft.server.v1_4_R1.PlayerConnection.a(PlayerConnection.java:863)
at net.minecraft.server.v1_4_R1.Packet3Chat.handle(Packet3Chat.java:44)
at net.minecraft.server.v1_4_R1.NetworkManager.i(NetworkManager.java:208)
at net.minecraft.server.v1_4_R1.NetworkManager.c(NetworkManager.java:344)
at net.minecraft.server.v1_4_R1.NetworkReaderThread.run(SourceFile:93)
Caused by: java.util.UnknownFormatConversionException: Conversion = 'u'
at org.bukkit.event.player.AsyncPlayerChatEvent.setFormat(AsyncPlayerChatEvent.java:82)
at org.mctourney.AutoReferee.listeners.TeamListener.chatMessage(TeamListener.java:69)
at sun.reflect.GeneratedMethodAccessor17.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:425)
... 9 more

I would hazard a guess that someone typed %u in their message. I just looked at my code for AsyncPlayerChatEvent. I've been using setFormat wrong for months and months. How was this not caught before?