Signs console error log

[19:07:50 ERROR]: Could not pass event PlayerInteractEvent to Signs v1.8
org.bukkit.event.EventException
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:302) ~[spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:509) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:494) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at org.bukkit.craftbukkit.v1_7_R4.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:242) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at net.minecraft.server.v1_7_R4.PlayerInteractManager.interact(PlayerInteractManager.java:382) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at net.minecraft.server.v1_7_R4.PlayerConnection.a(PlayerConnection.java:662) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at net.minecraft.server.v1_7_R4.PacketPlayInBlockPlace.a(PacketPlayInBlockPlace.java:50) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at net.minecraft.server.v1_7_R4.PacketPlayInBlockPlace.handle(PacketPlayInBlockPlace.java:86) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at net.minecraft.server.v1_7_R4.NetworkManager.a(NetworkManager.java:186) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at net.minecraft.server.v1_7_R4.ServerConnection.c(ServerConnection.java:81) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at net.minecraft.server.v1_7_R4.MinecraftServer.v(MinecraftServer.java:734) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at net.minecraft.server.v1_7_R4.DedicatedServer.v(DedicatedServer.java:289) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at net.minecraft.server.v1_7_R4.MinecraftServer.u(MinecraftServer.java:584) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at net.minecraft.server.v1_7_R4.MinecraftServer.run(MinecraftServer.java:490) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        at net.minecraft.server.v1_7_R4.ThreadServerApplication.run(SourceFile:628) [spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
Caused by: java.lang.IncompatibleClassChangeError: Found interface com.sk89q.worldguard.protection.ApplicableRegionSet, but class was expected
        at com.jofkos.signs.plugin.WorldGuardPlugin.canBuild(WorldGuardPlugin.java:19) ~[?:?]
        at com.jofkos.signs.utils.API.canBuild(API.java:52) ~[?:?]
        at com.jofkos.signs.utils.API.canBuild(API.java:42) ~[?:?]
        at com.jofkos.signs.listeners.EditListener.onClickEditSign(EditListener.java:29) ~[?:?]
        at sun.reflect.GeneratedMethodAccessor134.invoke(Unknown Source) ~[?:?]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.7.0_72]
        at java.lang.reflect.Method.invoke(Method.java:606) ~[?:1.7.0_72]
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:298) ~[spigot.jar:git-Spigot-1.7.9-R0.2-207-g03373bb]
        ... 15 more