DoubleXP Error

2013-03-30 14:07:43 [INFO] Starting minecraft server version 1.5.1
2013-03-30 14:07:43 [INFO] Loading properties
2013-03-30 14:07:43 [INFO] Default game type: SURVIVAL
2013-03-30 14:07:43 [INFO] Generating keypair
2013-03-30 14:07:44 [INFO] Starting Minecraft server on *:25565
2013-03-30 14:07:44 [INFO] This server is running CraftBukkit version git-Bukkit-1.4.7-R1.0-83-gb08af02-b2723jnks (MC: 1.5.1) (Implementing API version 1.5.1-R0.1-SNAPSHOT)
2013-03-30 14:07:44 [INFO] [PermissionsEx] sql backend registered!
2013-03-30 14:07:45 [INFO] [PermissionsEx] file backend registered!
2013-03-30 14:07:45 [INFO] [PermissionsEx] PermissionEx plugin initialized.
2013-03-30 14:07:45 [SEVERE] Could not load 'plugins/DoubleXP.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError: ws/gandy/DoubleXP/Main : Unsupported major.minor version 51.0
	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_R2.CraftServer.loadPlugins(CraftServer.java:239)
	at org.bukkit.craftbukkit.v1_5_R2.CraftServer.<init>(CraftServer.java:217)
	at net.minecraft.server.v1_5_R2.PlayerList.<init>(PlayerList.java:55)
	at net.minecraft.server.v1_5_R2.DedicatedPlayerList.<init>(SourceFile:11)
	at net.minecraft.server.v1_5_R2.DedicatedServer.init(DedicatedServer.java:105)
	at net.minecraft.server.v1_5_R2.MinecraftServer.run(MinecraftServer.java:379)
	at net.minecraft.server.v1_5_R2.ThreadServerApplication.run(SourceFile:573)
Caused by: java.lang.UnsupportedClassVersionError: ws/gandy/DoubleXP/Main : Unsupported major.minor version 51.0
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
	at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)
	at java.net.URLClassLoader.access$000(URLClassLoader.java:73)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:212)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
	at org.bukkit.plugin.java.PluginClassLoader.findClass0(PluginClassLoader.java:80)
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:53)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:266)
	at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:173)
	... 9 more