Plugin Help What is this?

Code:

[16:07:22] [Server thread/ERROR]: **** THIS IS NOT AN ISSUE TO DO WITH PER WORLD PLUGINS ****
Could not pass event PlayerInteractEvent to CoreProtect v2.13.1
org.bukkit.event.EventException
    at me.incomprehendable.dev.pwp.transparentlisteners.PerWorldPluginLoader$1.execute(PerWorldPluginLoader.java:118) ~[?:?]
    at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at me.incomprehendable.dev.pwp.transparentlisteners.PWPRegisteredListener.callEvent(PWPRegisteredListener.java:28) [PerWorldPlugins.jar:?]
    at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:501) [1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:486) [1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at org.bukkit.craftbukkit.v1_8_R3.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:210) [1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at net.minecraft.server.v1_8_R3.PlayerInteractManager.interact(PlayerInteractManager.java:462) [1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at net.minecraft.server.v1_8_R3.PlayerConnection.a(PlayerConnection.java:728) [1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at net.minecraft.server.v1_8_R3.PacketPlayInBlockPlace.a(PacketPlayInBlockPlace.java:52) [1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at net.minecraft.server.v1_8_R3.PacketPlayInBlockPlace.a(PacketPlayInBlockPlace.java:1) [1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at net.minecraft.server.v1_8_R3.PlayerConnectionUtils$1.run(SourceFile:13) [1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_111]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_111]
    at net.minecraft.server.v1_8_R3.SystemUtils.a(SourceFile:44) [1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:673) [1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:335) [1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:629) [1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:537) [1.8.8_bukkit.jar:git-Bukkit-62a2169]
    at java.lang.Thread.run(Thread.java:745) [?:1.8.0_111]
Caused by: java.lang.NoSuchFieldError: END_CRYSTAL
    at net.coreprotect.listener.PlayerListener.onPlayerInteract_Monitor(PlayerListener.java:626) ~[?:?]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_111]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_111]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_111]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_111]
    at me.incomprehendable.dev.pwp.transparentlisteners.PerWorldPluginLoader$1.execute(PerWorldPluginLoader.java:116) ~[?:?]
    ... 18 more