Bukkit

[SEVERE] Could not load 'plugins/RebalanceVillagers-1.5.1.1-SNAPSHOT.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.NoClassDefFoundError: net/minecraft/server/v1_5_R2/World
    at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:184)
    at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:305)
    at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:230)
    at org.bukkit.craftbukkit.v1_5_R3.CraftServer.loadPlugins(CraftServer.java:239)
    at org.bukkit.craftbukkit.v1_5_R3.CraftServer.<init>(CraftServer.java:217)
    at net.minecraft.server.v1_5_R3.PlayerList.<init>(PlayerList.java:55)
    at net.minecraft.server.v1_5_R3.DedicatedPlayerList.<init>(SourceFile:11)
    at net.minecraft.server.v1_5_R3.DedicatedServer.init(DedicatedServer.java:106)
    at net.minecraft.server.v1_5_R3.MinecraftServer.run(MinecraftServer.java:382)
    at net.minecraft.server.v1_5_R3.ThreadServerApplication.run(SourceFile:573)
Caused by: java.lang.NoClassDefFoundError: net/minecraft/server/v1_5_R2/World
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Unknown Source)
    at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:173)
    ... 9 more
Caused by: java.lang.ClassNotFoundException: net.minecraft.server.v1_5_R2.World
    at org.bukkit.plugin.java.PluginClassLoader.findClass0(PluginClassLoader.java:70)
    at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:53)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    ... 12 more