Server startup error; BlockPerms

2013-01-31 18:27:45 [SEVERE] Could not load 'plugins/BlockPerms.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError: main/BlockPerms/BlockPermsMain : 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_4_R1.CraftServer.loadPlugins(CraftServer.java:239)
        at org.bukkit.craftbukkit.v1_4_R1.CraftServer.<init>(CraftServer.java:217)
        at net.minecraft.server.v1_4_R1.PlayerList.<init>(PlayerList.java:55)
        at net.minecraft.server.v1_4_R1.DedicatedPlayerList.<init>(SourceFile:11)
        at net.minecraft.server.v1_4_R1.DedicatedServer.init(DedicatedServer.java:104)
        at net.minecraft.server.v1_4_R1.MinecraftServer.run(MinecraftServer.java:399)
        at net.minecraft.server.v1_4_R1.ThreadServerApplication.run(SourceFile:849)
Caused by: java.lang.UnsupportedClassVersionError: main/BlockPerms/BlockPermsMain : Unsupported major.minor version 51.0
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
        at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        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:307)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Class.java:247)
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:173)
        ... 9 more