The following forum message was posted by fabioz at http://sourceforge.net/projects/pydev/forums/forum/293649/topic/4410576:
The /Lib folder is not a folder inside your Jython.jar, it's a folder that's
usually along the .jar file.
I just took a quick look at grinder and it seems it doesn't ship with it, but
they point that you should have it if you want to do anything that uses the
Jython llibs (which is your case).
So, follow their instructions from:
http://grinder.sourceforge.net/faq.html#jython-libraries and add the jython
you installed (not the default that comes with grinder) + the needed grinder