Code:

14.02 20:34:29 [Server] INFO at net.minecraft.server.ThreadServerApplication.run(SourceFile:465) 14.02 20:34:29 [Server] INFO at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:408) 14.02 20:34:29 [Server] INFO at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:148) 14.02 20:34:29 [Server] INFO at net.minecraft.server.ServerConfigurationManager.<init>(ServerConfigurationManager.java:52) 14.02 20:34:29 [Server] INFO at org.bukkit.craftbukkit.CraftServer.<init>(CraftServer.java:140) 14.02 20:34:29 [Server] INFO at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:164) 14.02 20:34:29 [Server] INFO at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:201) 14.02 20:34:29 [Server] INFO at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:286) 14.02 20:34:29 [Server] INFO at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:131) 14.02 20:34:29 [Server] INFO at java.lang.Class.forName(Class.java:264) 14.02 20:34:29 [Server] INFO at java.lang.Class.forName0(Native Method) 14.02 20:34:29 [Server] INFO at java.lang.ClassLoader.loadClass(ClassLoader.java:266) 14.02 20:34:29 [Server] INFO at java.lang.ClassLoader.loadClass(ClassLoader.java:321) 14.02 20:34:29 [Server] INFO at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:29) 14.02 20:34:29 [Server] INFO at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:41) 14.02 20:34:29 [Server] INFO at java.net.URLClassLoader.findClass(URLClassLoader.java:205) 14.02 20:34:29 [Server] INFO at java.security.AccessController.doPrivileged(Native Method) 14.02 20:34:29 [Server] INFO at java.net.URLClassLoader$1.run(URLClassLoader.java:212) 14.02 20:34:29 [Server] INFO at java.net.URLClassLoader.access$000(URLClassLoader.java:73) 14.02 20:34:29 [Server] INFO at java.net.URLClassLoader.defineClass(URLClassLoader.java:277) 14.02 20:34:29 [Server] INFO at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) 14.02 20:34:29 [Server] INFO at java.lang.ClassLoader.defineClass(ClassLoader.java:634) 14.02 20:34:29 [Server] INFO at java.lang.ClassLoader.defineClass1(Native Method) 14.02 20:34:29 [Server] INFO java.lang.UnsupportedClassVersionError: me/Prometheus/DeGriefer/DeGriefer : Unsupported major.minor version 51.0 14.02 20:34:29 [Server] SEVERE Could not load 'plugins/DeGriefer.jar' in folder 'plugins':