After upgrading, did you also update your Java installation and reconfigure LW in your firewall (if you run XP, the built-in firewall) as described in connection problems -click first:
http://www.gnutellaforums.com/showthread.php?t=51361
To update your Java, you have to uninstall all previous versions, reboot, download the newest version from here using the JRE offline installer:
http://java.sun.com/j2se/1.5.0/download.jsp
Install it and reboot again.
If you had an older version of LW, you may also delete the preference folder of the old (and as precausion of the new as well) version as described here in Point #2 & 3 in Fixes for Limewire:
http://www.gnutellaforums.com/showth...threadid=36420 