Plugin Error

[04:59:08 INFO]: This server is running CraftBukkit version git-Bukkit-1.7.2-R0.2-b2974jnks (MC: 1.7.2) (Implementing API version 1.7.2-R0.2)
[04:59:09 ERROR]: Could not load 'plugins/JustBlood.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError: fr/gravenilvec/JustBlood/JustBlood : 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: fr/gravenilvec/JustBlood/JustBlood : Unsupported major.minor version 51.0
	at java.lang.ClassLoader.defineClass1(Native Method) ~[?:1.6.0_65]
	at java.lang.ClassLoader.defineClassCond(ClassLoader.java:637) ~[?:1.6.0_65]
	at java.lang.ClassLoader.defineClass(ClassLoader.java:621) ~[?:1.6.0_65]
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141) ~[?:1.6.0_65]
	at java.net.URLClassLoader.defineClass(URLClassLoader.java:283) ~[?:1.6.0_65]
	at java.net.URLClassLoader.access$000(URLClassLoader.java:58) ~[?:1.6.0_65]
	at java.net.URLClassLoader$1.run(URLClassLoader.java:197) ~[?:1.6.0_65]
	at java.security.AccessController.doPrivileged(Native Method) ~[?:1.6.0_65]
	at java.net.URLClassLoader.findClass(URLClassLoader.java:190) ~[?:1.6.0_65]
	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(ClassLoader.java:306) ~[?:1.6.0_65]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:247) ~[?:1.6.0_65]
	at java.lang.Class.forName0(Native Method) ~[?:1.6.0_65]
	at java.lang.Class.forName(Class.java:249) ~[?:1.6.0_65]
	at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:173) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
	... 9 more
[04:59:09 INFO]: Preparing level "world"
[04:59:09 INFO]: Preparing start region for level 0 (Seed: -4602580968022132736)
[04:59:10 INFO]: Preparing start region for level 1 (Seed: -4602580968022132736)
[04:59:11 INFO]: Preparing start region for level 2 (Seed: -4602580968022132736)
[04:59:11 INFO]: Server permissions file permissions.yml is empty, ignoring it
[04:59:11 INFO]: Done (2.339s)! For help, type "help" or "?"
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