Startup Error

[09:50:38] [Server thread/ERROR]: Error occurred while enabling IsleWorldGen v5.1 (Is it up to date?)
java.lang.NoClassDefFoundError: net/minecraft/server/v1_7_R4/TileEntity
	at org.tilegames.hexicube.bukkit.isle.IslandWorldGeneration.loadOres(IslandWorldGeneration.java:397) ~[?:?]
	at org.tilegames.hexicube.bukkit.isle.IslandWorldGeneration.onEnable(IslandWorldGeneration.java:179) ~[?:?]
	at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:321) ~[spigot.jar:git-Spigot-2b97a38-e8efbb8]
	at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:335) [spigot.jar:git-Spigot-2b97a38-e8efbb8]
	at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:405) [spigot.jar:git-Spigot-2b97a38-e8efbb8]
	at org.bukkit.craftbukkit.v1_8_R1.CraftServer.loadPlugin(CraftServer.java:354) [spigot.jar:git-Spigot-2b97a38-e8efbb8]
	at org.bukkit.craftbukkit.v1_8_R1.CraftServer.enablePlugins(CraftServer.java:314) [spigot.jar:git-Spigot-2b97a38-e8efbb8]
	at net.minecraft.server.v1_8_R1.DedicatedServer.init(DedicatedServer.java:153) [spigot.jar:git-Spigot-2b97a38-e8efbb8]
	at net.minecraft.server.v1_8_R1.MinecraftServer.run(MinecraftServer.java:494) [spigot.jar:git-Spigot-2b97a38-e8efbb8]
	at java.lang.Thread.run(Unknown Source) [?:1.8.0_25]
Caused by: java.lang.ClassNotFoundException: net.minecraft.server.v1_7_R4.TileEntity
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:91) ~[spigot.jar:git-Spigot-2b97a38-e8efbb8]
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:86) ~[spigot.jar:git-Spigot-2b97a38-e8efbb8]
	at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_25]
	at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_25]
	... 10 more