Error 8

[13:31:48] [Server thread/ERROR]: Could not load 'plugins\AdminGUI.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError: de/bigcool200/admingui/Main : Unsupported major.minor version 52.0
    at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:131) ~[craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
    at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:328) ~[craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
    at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:251) [craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
    at org.bukkit.craftbukkit.v1_7_R4.CraftServer.loadPlugins(CraftServer.java:364) [craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
    at org.bukkit.craftbukkit.v1_7_R4.CraftServer.<init>(CraftServer.java:326) [craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
    at net.minecraft.server.v1_7_R4.PlayerList.<init>(PlayerList.java:68) [craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
    at net.minecraft.server.v1_7_R4.DedicatedPlayerList.<init>(SourceFile:14) [craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
    at net.minecraft.server.v1_7_R4.DedicatedServer.init(DedicatedServer.java:133) [craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
    at net.minecraft.server.v1_7_R4.MinecraftServer.run(MinecraftServer.java:436) [craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
    at net.minecraft.server.v1_7_R4.ThreadServerApplication.run(SourceFile:628) [craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
Caused by: java.lang.UnsupportedClassVersionError: de/bigcool200/admingui/Main : Unsupported major.minor version 52.0
    at java.lang.ClassLoader.defineClass1(Native Method) ~[?:1.7.0_45]
    at java.lang.ClassLoader.defineClass(Unknown Source) ~[?:1.7.0_45]
    at java.security.SecureClassLoader.defineClass(Unknown Source) ~[?:1.7.0_45]
    at java.net.URLClassLoader.defineClass(Unknown Source) ~[?:1.7.0_45]
    at java.net.URLClassLoader.access$100(Unknown Source) ~[?:1.7.0_45]
    at java.net.URLClassLoader$1.run(Unknown Source) ~[?:1.7.0_45]
    at java.net.URLClassLoader$1.run(Unknown Source) ~[?:1.7.0_45]
    at java.security.AccessController.doPrivileged(Native Method) ~[?:1.7.0_45]
    at java.net.URLClassLoader.findClass(Unknown Source) ~[?:1.7.0_45]
    at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:77) ~[craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
    at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:62) ~[craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
    at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.7.0_45]
    at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.7.0_45]
    at java.lang.Class.forName0(Native Method) ~[?:1.7.0_45]
    at java.lang.Class.forName(Unknown Source) ~[?:1.7.0_45]
    at org.bukkit.plugin.java.PluginClassLoader.<init>(PluginClassLoader.java:40) ~[craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
    at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:127) ~[craftbukkit.jar:git-Bukkit-1.7.9-R0.2-17-g3833911-b3106jnks]
    ... 9 more