Bukkit

Any ideas whats causing this error?

[10:33:52] [Server thread/ERROR]: Could not pass event PlayerDeathEvent to blFriends v0.9.7c
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.callPlayerDeathEvent(CraftEventFactory.java:381) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.EntityPlayer.die(EntityPlayer.java:407) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.EntityLiving.damageEntity(EntityLiving.java:806) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.EntityHuman.damageEntity(EntityHuman.java:801) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.EntityPlayer.damageEntity(EntityPlayer.java:486) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.EntityArrow.s_(EntityArrow.java:244) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.World.entityJoinedWorld(World.java:1604) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.World.g(World.java:1579) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.World.tickEntities(World.java:1422) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.WorldServer.tickEntities(WorldServer.java:576) [minecraft_server.jar:git-Spigot-c3c767f-33d5de3]
    at net.minecraft.server.v1_8_R1.MinecraftServer.z(MinecraftServer.java:772) [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 net.blcraft.blfriends.RegionSupport.MobBonusXP(RegionSupport.java:107) ~[?:?]
    at sun.reflect.GeneratedMethodAccessor724.invoke(Unknown Source) ~[?:?]
    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

Please provide any additional information below.