Use Hotline to download someone else's older vers.
Worked for me!
I was downloading Ludacris' "move, bitch" within 10 minutes of my humble solution. I got the same ****:

Fatal application error:

unable to launch java application

unable to locate the application's main class. The class 'com.limegroup.gnutella.gui.main' must be public and have 'public static void main(String[])' method. (LAX)

good luck to all.