Bukkit

Hello, when I start my Server with this Plugin I recieve this error:
2011-11-19 20:40:51 [SEVERE] Could not load 'plugins\RewardMe.jar' in folder 'plugins':
java.lang.UnsupportedClassVersionError: me/se1by/RewardMe/RewardMe : Unsupported major.minor version 51.0
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClassCond(Unknown Source)
    at java.lang.ClassLoader.defineClass(Unknown Source)
    at java.security.SecureClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.access$000(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:36)
    at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:24)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Unknown Source)
    at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:170)
    at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:215)
    at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:136)
    at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:136)
    at org.bukkit.craftbukkit.CraftServer.<init>(CraftServer.java:112)
    at net.minecraft.server.ServerConfigurationManager.<init>(ServerConfigurationManager.java:52)
    at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:136)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:348)
    at net.minecraft.server.ThreadServerApplication.run(SourceFile:417)

I am using CB #1337, RewardMe 1.1, Spout #510, Register 1.5, Iconom 6.0.8 and more.

Somehow, I wasN#t contacted by bukkit so I didn't saw this earlier. You run another java version than it's compiled for. Download the new version and it should work.