Unsupported major.minor version 51.0 Error Please help

hello guys,
often when i try to use plugins i get this error "Unsupported major.minor version 51.0"
please help me:

bowspleef:
17:03:37 [SEVERE] Could not load 'plugins/BowSpleef.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError: com/untoldadventures/bowspleef/BowSpleef : Unsupported major.minor version 51.0
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:184)
at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:306)
at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:230)
at org.bukkit.craftbukkit.v1_6_R2.CraftServer.loadPlugins(CraftServer.java:243)
at org.bukkit.craftbukkit.v1_6_R2.CraftServer.reload(CraftServer.java:610)
at org.bukkit.Bukkit.reload(Bukkit.java:275)
at org.bukkit.command.defaults.ReloadCommand.execute(ReloadCommand.java:24)
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:190)
at org.bukkit.craftbukkit.v1_6_R2.CraftServer.dispatchCommand(CraftServer.java:527)
at org.bukkit.craftbukkit.v1_6_R2.CraftServer.dispatchServerCommand(CraftServer.java:516)
at net.minecraft.server.v1_6_R2.DedicatedServer.ar(DedicatedServer.java:275)
at net.minecraft.server.v1_6_R2.DedicatedServer.t(DedicatedServer.java:240)
at net.minecraft.server.v1_6_R2.MinecraftServer.s(MinecraftServer.java:481)
at net.minecraft.server.v1_6_R2.MinecraftServer.run(MinecraftServer.java:413)
at net.minecraft.server.v1_6_R2.ThreadServerApplication.run(SourceFile:582)
Caused by: java.lang.UnsupportedClassVersionError: com/untoldadventures/bowspleef/BowSpleef : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
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:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:249)
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:173)
... 14 more
reward token:
17:03:37 [SEVERE] Could not load 'plugins/RewardToken.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError: com/yahoo/firehawks_general/RewardToken/RewardToken : Unsupported major.minor version 51.0
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:184)
at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:306)
at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:230)
at org.bukkit.craftbukkit.v1_6_R2.CraftServer.loadPlugins(CraftServer.java:243)
at org.bukkit.craftbukkit.v1_6_R2.CraftServer.reload(CraftServer.java:610)
at org.bukkit.Bukkit.reload(Bukkit.java:275)
at org.bukkit.command.defaults.ReloadCommand.execute(ReloadCommand.java:24)
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:190)
at org.bukkit.craftbukkit.v1_6_R2.CraftServer.dispatchCommand(CraftServer.java:527)
at org.bukkit.craftbukkit.v1_6_R2.CraftServer.dispatchServerCommand(CraftServer.java:516)
at net.minecraft.server.v1_6_R2.DedicatedServer.ar(DedicatedServer.java:275)
at net.minecraft.server.v1_6_R2.DedicatedServer.t(DedicatedServer.java:240)
at net.minecraft.server.v1_6_R2.MinecraftServer.s(MinecraftServer.java:481)
at net.minecraft.server.v1_6_R2.MinecraftServer.run(MinecraftServer.java:413)
at net.minecraft.server.v1_6_R2.ThreadServerApplication.run(SourceFile:582)
Caused by: java.lang.UnsupportedClassVersionError: com/yahoo/firehawks_general/RewardToken/RewardToken : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
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:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:249)
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:173)
... 14 more


i am running on java 7 and have used my friends start.command (i am on a mac) and there whole folder works for them, not for me though

 

You're not ;D
Type java -version in a terminal and post the output

 

Last login: Fri Aug 16 12:20:51 on console
(null):~ jacksmac$ java -version
java version "1.6.0_51"
Java(TM) SE Runtime Environment (build 1.6.0_51-b11-457-11M4509)
Java HotSpot(TM) 64-Bit Server VM (build 20.51-b01-457, mixed mode)
(null):~ jacksmac$

Sorry for wasting you time,
i tryed to download java 7 so many times and i just assumed it worked, Thanks SO MUCH

but how do i make it java 7 i have tryed updating it and it doesnt work, it says in the System preferences > Java folder
that i am on java 7 but when i do the "java -version" it still says 1.6 please help me, thanks

 

Follow this guide please:
http://docs.oracle.com/javase/7/docs/webnotes/install/mac/mac-jdk.html
The background: