I'm just another user like you, but I'm also on a Mac w/OSX (10.2.6) and just upgraded to the newest version of LW and had the same problem you are. Try running a search on this board for "connection problem" or "can't connect." Apparently, lots of folks had the same problem as well. Several fixes are recommended in different threads, but changing my ports like "somekid" did worked for me.

"I found the problem under tools/options - advanced/firewalls and ports. All of the numbers were different for some reason or another..but now my firewall and port numbers are both 6348..."
(see "can't connect" thread started by somekid)

One of the fixes your search turns up should work for you. Good Luck!

P.S. If all else fails, run a search on LW under programs for Acquisition (sorry, Limewire). I have both and AQ seems a wee bit more stable, but searches don't seem to turn up as many results.