Could be two things:
first it sounds like a license issue; read here on how to change this:
http://www.gnutellaforums.com/showth...176#post154176
Second a possible Java issue. Uninstall LW and all Java versions on your system. Reboot and then download the JRE offline installer of the newest Java version from here:
http://java.sun.com/j2se/1.5.0/download.jsp
Install it and reboot again, then reinstall LW.
