error

[10:45:28] [Server thread/INFO]: [LorinthsRpgMobs]: Found World Guard!
[10:45:28] [Server thread/WARN]: [LorinthsRpgMobs] Task #19 for LorinthsRpgMobs vDEV-2.0 generated an exception
java.lang.NoClassDefFoundError: net/minecraft/server/v1_7_R1/EntitySkeleton
	at me.Lorinth.SpawnerMobs.CustomSpawnerMob.<clinit>(CustomSpawnerMob.java:24) ~[?:?]
	at me.Lorinth.MobDifficulty.MobDifficulty.registerCustomMobs(MobDifficulty.java:431) ~[?:?]
	at me.Lorinth.MobDifficulty.MobDifficulty.start(MobDifficulty.java:196) ~[?:?]
	at me.Lorinth.MobDifficulty.MobDifficulty$1.run(MobDifficulty.java:167) ~[?:?]
	at org.bukkit.craftbukkit.v1_7_R3.scheduler.CraftTask.run(CraftTask.java:53) ~[minecraft_server.jar:git-Bukkit-1.7.9-R0.1-10-g8688bd4-b3092jnks]
	at org.bukkit.craftbukkit.v1_7_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:345) [minecraft_server.jar:git-Bukkit-1.7.9-R0.1-10-g8688bd4-b3092jnks]
	at net.minecraft.server.v1_7_R3.MinecraftServer.v(MinecraftServer.java:600) [minecraft_server.jar:git-Bukkit-1.7.9-R0.1-10-g8688bd4-b3092jnks]
	at net.minecraft.server.v1_7_R3.DedicatedServer.v(DedicatedServer.java:260) [minecraft_server.jar:git-Bukkit-1.7.9-R0.1-10-g8688bd4-b3092jnks]
	at net.minecraft.server.v1_7_R3.MinecraftServer.u(MinecraftServer.java:558) [minecraft_server.jar:git-Bukkit-1.7.9-R0.1-10-g8688bd4-b3092jnks]
	at net.minecraft.server.v1_7_R3.MinecraftServer.run(MinecraftServer.java:469) [minecraft_server.jar:git-Bukkit-1.7.9-R0.1-10-g8688bd4-b3092jnks]
	at net.minecraft.server.v1_7_R3.ThreadServerApplication.run(SourceFile:628) [minecraft_server.jar:git-Bukkit-1.7.9-R0.1-10-g8688bd4-b3092jnks]
Caused by: java.lang.ClassNotFoundException: net.minecraft.server.v1_7_R1.EntitySkeleton
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:67) ~[minecraft_server.jar:git-Bukkit-1.7.9-R0.1-10-g8688bd4-b3092jnks]
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:62) ~[minecraft_server.jar:git-Bukkit-1.7.9-R0.1-10-g8688bd4-b3092jnks]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:425) ~[?:1.7.0_65]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:358) ~[?:1.7.0_65]
	... 11 more