Bukkit

15:47:57 [SEVERE] Could not pass event org.bukkit.event.block.BlockFromToEvent to ClayGen
org.bukkit.event.EventException
        at org.bukkit.plugin.java.JavaPluginLoader$103.execute(JavaPluginLoader.java:1026)
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:61)
        at org.bukkit.plugin.TimedRegisteredListener.callEvent(TimedRegisteredListener.java:30)
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:460)
        at net.minecraft.server.BlockFlowing.a(BlockFlowing.java:140)
        at net.minecraft.server.World.k(World.java:2002)
        at net.minecraft.server.World.doTick(World.java:1752)
        at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:524)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:435)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:465)
Caused by: java.lang.reflect.InvocationTargetException
        at sun.reflect.GeneratedMethodAccessor77.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:601)
        at org.bukkit.plugin.java.JavaPluginLoader$103.execute(JavaPluginLoader.java:1024)
        ... 9 more