Bukkit

What steps will reproduce the problem?
1.Any time I run or reload the server

What is the expected output? What do you see instead?

I thought it would just run fine, but I got an error in my server log and the plugin is not running.

What version of the product are you using?

I'm using  GriefAlert V. 2.3 for 1.6.2, the latest version of Vault, and Bukkit version 1.6.2-R0.1

Do you have an error log of what happened?

Yup. Here:

[SEVERE] Could not load 'plugins\GriefAlert.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError: me/noraaron1/GriefAlert/GriefAlert : 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_6_R2.CraftServer.loadPlugins(CraftServer.java:239)
    at org.bukkit.craftbukkit.v1_6_R2.CraftServer.<init>(CraftServer.java:217)
    at net.minecraft.server.v1_6_R2.PlayerList.<init>(PlayerList.java:56)
    at net.minecraft.server.v1_6_R2.DedicatedPlayerList.<init>(SourceFile:11)
    at net.minecraft.server.v1_6_R2.DedicatedServer.init(DedicatedServer.java:106)
    at net.minecraft.server.v1_6_R2.MinecraftServer.run(MinecraftServer.java:391)
    at net.minecraft.server.v1_6_R2.ThreadServerApplication.run(SourceFile:582)
Caused by: java.lang.UnsupportedClassVersionError: me/noraaron1/GriefAlert/GriefAlert : 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.findClass0(PluginClassLoader.java:80)
    at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:53)
    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:173)
    ... 9 more

Please provide any additional information below.

I was wondering if I have a plugin that might clash with this one. Here's the plugins I have:

ChatPing
Commands
DisguiseCraft
GriefAlert (of course)
HeadHunter
HeroicDeathPlus
InfinityDispencer
LaunchPads
Multiverse-Core, -Inventories, and -Portals, -2.5
Namer
OcarinaSong
PermissionsEx
ProtocolLib
SparkTrail
TagAPI
TARDIS
Vault (Also needed)
ZombieRessurection

What java are you runing on?