This happens to me on linux after a download of jruby:
[23:1316][rdp@ilab2:~/dev/downloads/jruby-1.1.4/bin]$ ./jruby
Exception in thread “main” java.lang.NoClassDefFoundError:
org/jruby/Main
Caused by: java.lang.ClassNotFoundException: org.jruby.Main
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
[23:1313][rdp@ilab2:~/dev/downloads/jruby-1.1.4/bin]$ java -version
java version “1.6.0_06”
Java™ SE Runtime Environment (build 1.6.0_06-b02)
Java HotSpot™ Server VM (build 10.0-b22, mixed mode)
help?
-=R