Voila je lance mon serveur (1.3)avec le plugin (1.3) tutorial sign et voila ce que j ai dans les logs

2012-08-07 22:19:55 [SEVERE] Could not load 'plugins\TutorialSigns.jar' in folder 'plugins' org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError: de/ronyzzn/tutorialsigns/TutorialSigns : Unsupported major.minor version 51.0 at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin
(JavaPluginLoader.java:155)
at org.bukkit.plugin.SimplePluginManager.loadPlugin(S
implePluginManager.java:305)
at org.bukkit.plugin.SimplePluginManager.loadPlugins(
SimplePluginManager.java:230)
at org.bukkit.craftbukkit.CraftServer.loadPlugins(Cra
ftServer.java:222)
at org.bukkit.craftbukkit.CraftServer.<init>(CraftSer
ver.java:198)
at net.minecraft.server.ServerConfigurationManagerAbs
tract.<init>(ServerConfigurationManagerAbstract.ja
va:50)
at net.minecraft.server.ServerConfigurationManager.<i
nit>(SourceFile:11)
at net.minecraft.server.DedicatedServer.init(Dedicate
dServer.java:105)
at net.minecraft.server.MinecraftServer.run(Minecraft
Server.java:380)
at net.minecraft.server.ThreadServerApplication.run(S
ourceFile:539)
Caused by: java.lang.UnsupportedClassVersionError: de/ronyzzn/tutorialsigns/TutorialSigns : 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(Unknow
n
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:41)
at org.bukkit.plugin.java.PluginClassLoader.findClass
(PluginClassLoader.java:29)
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:144)
... 9 more

Pourquoi ? Solution ?
Metci