Bukkit

I get this error every time I fire an arrow of any type. Any ideas what I am doing wrong?

[08:23:41] [Server thread/ERROR]: Could not pass event EntityShootBowEvent to TheArcher v2.4.2
org.bukkit.event.EventException
    at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:305) ~[minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:502) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:487) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at org.bukkit.craftbukkit.v1_8_R1.event.CraftEventFactory.callEntityShootBowEvent(CraftEventFactory.java:244) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.ItemBow.a(ItemBow.java:61) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.ItemStack.b(ItemStack.java:504) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.EntityHuman.bT(EntityHuman.java:108) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.PlayerConnection.a(PlayerConnection.java:570) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.PacketPlayInBlockDig.a(SourceFile:40) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.PacketPlayInBlockDig.a(SourceFile:10) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.PacketHandleTask.run(SourceFile:13) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_40]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_40]
    at net.minecraft.server.v1_8_R1.MinecraftServer.z(MinecraftServer.java:696) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.DedicatedServer.z(DedicatedServer.java:316) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.MinecraftServer.y(MinecraftServer.java:634) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.MinecraftServer.run(MinecraftServer.java:537) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at java.lang.Thread.run(Thread.java:745) [?:1.8.0_40]
Caused by: java.lang.IncompatibleClassChangeError: Found interface com.sk89q.worldguard.protection.ApplicableRegionSet, but class was expected
    at com.gmail.josemanuelgassin.TheArcher.Util_WG.jugadorEnRegión(Util_WG.java:15) ~[?:?]
    at com.gmail.josemanuelgassin.TheArcher.Listener_Disparo.JugadorDisparaFlecha(Listener_Disparo.java:55) ~[?:?]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_40]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_40]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_40]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[?:1.8.0_40]
    at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:301) ~[minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    ... 18 more