Delete your preferences folder, instructions here
http://www.gnutellaforums.com/showth...threadid=36420
(you'll have to reset your preferences in tools > options afterwards. If you're not sure of your settings, go through & make a note of them first)

If this doesn't help, uninstall your Java & reinstall using the link to offline installer in the above thread. Or you can try the new JRE beta
http://java.sun.com/javase/6/download.jsp