title: Rubymine startup error java.lang.NoClassDefFoundError: com/intellij/util/lang/UrlClassLoader
body: <p>I am using Ubuntu 11.04, when i start RubyMine3.1 it gave this error.</p>
  
  <pre><code>Exception in thread "main" java.lang.NoClassDefFoundError: com/intellij/util/lang/UrlClassLoader
      at com.intellij.idea.Main.main(Main.java:55)
  Caused by: java.lang.ClassNotFoundException: com.intellij.util.lang.UrlClassLoader
      at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
      at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
      at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
      at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
      ... 1 more
  </code></pre>
  
  <p>I tried every thing, i also have sun-java installed, set it default by update-java-alternatives, also my JAVA_HOME, JDK_HOME, RUBYMINE_JDK points to the sun-java directory, but still no success.</p>
  
  <p>Does any one have any idea about it?</p>