When you deleted the preferences folder, did you also look for a folder in the old location (folder named .limewire)? When you started LW, did it run through the setup wizard again?

Have you also tried replacing the gnutella.net file, which is found within the hidden LimeWire folder? If not, there's more info here.
http://www.gnutellaforums.com/connec...t-fix-try.html
http://www.gnutellaforums.com/connec...tml#post296950