Did you also update your Java? Besides from which older version did you update from? You might have to delete the old preference folder as described here in #2 & 3 in Fixes for Limewire:
http://www.gnutellaforums.com/showth...threadid=36420
If the deletion of the folder doesn't solve the problem, 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.