[23:22:23] [Server thread/ERROR]: Could not load 'plugins\menubook.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError: nl/itsjustbjarn/plugins/MenuBook/MenuBook : Unsupported major.minor version 51.0
    at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:184) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:308) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:231) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at org.bukkit.craftbukkit.v1_7_R1.CraftServer.loadPlugins(CraftServer.java:255) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at org.bukkit.craftbukkit.v1_7_R1.CraftServer.<init>(CraftServer.java:233) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.PlayerList.<init>(PlayerList.java:63) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.DedicatedPlayerList.<init>(SourceFile:14) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.DedicatedServer.init(DedicatedServer.java:126) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.MinecraftServer.run(MinecraftServer.java:424) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.ThreadServerApplication.run(SourceFile:617) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
Caused by: java.lang.UnsupportedClassVersionError: nl/itsjustbjarn/plugins/MenuBook/MenuBook : Unsupported major.minor version 51.0
    at java.lang.ClassLoader.defineClass1(Native Method) ~[?:1.6.0_30]
    at java.lang.ClassLoader.defineClassCond(Unknown Source) ~[?:1.6.0_30]
    at java.lang.ClassLoader.defineClass(Unknown Source) ~[?:1.6.0_30]
    at java.security.SecureClassLoader.defineClass(Unknown Source) ~[?:1.6.0_30]
    at java.net.URLClassLoader.defineClass(Unknown Source) ~[?:1.6.0_30]
    at java.net.URLClassLoader.access$000(Unknown Source) ~[?:1.6.0_30]
    at java.net.URLClassLoader$1.run(Unknown Source) ~[?:1.6.0_30]
    at java.security.AccessController.doPrivileged(Native Method) ~[?:1.6.0_30]
    at java.net.URLClassLoader.findClass(Unknown Source) ~[?:1.6.0_30]
    at org.bukkit.plugin.java.PluginClassLoader.findClass0(PluginClassLoader.java:80) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:53) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.6.0_30]
    at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.6.0_30]
    at java.lang.Class.forName0(Native Method) ~[?:1.6.0_30]
    at java.lang.Class.forName(Unknown Source) ~[?:1.6.0_30]
    at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:173) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    ... 9 more