InvalidPluginException thrown by bukkit when loading RPG essentials in 1.5.2-R0.1 and b2778

[kenjindomini]

I've tried to load it in both the 1.5.2 beta build and the b2778 dev build and I get the same exception:

10:39:29 [SEVERE] Could not load 'plugins\RpgEssentials.jar' in folder 'plugins'

org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError
: me/duckdoom5/RpgEssentials/RpgEssentials : Unsupported major.minor version 51.
0
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:184)
at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.
java:305)
at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager
.java:254)
at org.bukkit.craftbukkit.v1_5_R3.CraftServer.loadPlugins(CraftServer.ja
va:239)
at org.bukkit.craftbukkit.v1_5_R3.CraftServer.(CraftServer.java:21
7)
at net.minecraft.server.v1_5_R3.PlayerList.(PlayerList.java:55)
at net.minecraft.server.v1_5_R3.DedicatedPlayerList.(SourceFile:11
)
at net.minecraft.server.v1_5_R3.DedicatedServer.init(DedicatedServer.jav
a:106)
at net.minecraft.server.v1_5_R3.MinecraftServer.run(MinecraftServer.java
:382)
at net.minecraft.server.v1_5_R3.ThreadServerApplication.run(SourceFile:5
73)
Caused by: java.lang.UnsupportedClassVersionError: me/duckdoom5/RpgEssentials/Rp
gEssentials : 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.j
ava:173)
... 9 more