JRE in Kubuntu doesn't allow me to run .jar file
<p>I am having trouble trying to run a .jar application on Kubuntu. I created an application in NetBeans in Windows and compiled it into a .jar file. First Windows couldn't find the main class. I searched the internet and fixed some registry values for the JRE and everything works fine now. However, the same problem has arised in Kubuntu, but I can't find anything of help. I've even tried uncompressing the .jar file and modifing the class path in the manifest file with many different path addresses, but nothing works.</p>

<p>Since the problem in Windows was on the JRE and not on my application, I think the same is happening in Kubuntu. An important note is that I've installed NetBeans on Kubuntu too and when I debug or run the application under Netbeans, it works fine, but when I compile it and try to run it with:</p>

<blockquote>
  <p>java -jar "MBoxTest.jar" </p>
</blockquote>

<p>I get the same errors I got on Windows including the final one that says it cannot find the main class:</p>

<pre><code>Exception in thread "main" java.lang.UnsupportedClassVersionError: my/mboxtestui/MBoxTestUI : Unsupported major.minor version 51.0
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)
    at java.net.URLClassLoader.access$000(URLClassLoader.java:73)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:212)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
Could not find the main class: my.mboxtestui.MBoxTestUI. Program will exit.
</code></pre>
