Delete your LW preferences folder. Instructions here
http://www.gnutellaforums.com/showth...threadid=36420
(you'll have to redo your settings within tools > options afterwards, so if you're not sure of your settings make a note of them).

Uninstall Java & reinstall using the offline installer. Instructions also in the above thread.
Or, you can try the Java 1.6 (JRE) beta here
http://java.sun.com/javase/6/download.jsp