You're using OSX & you have your firewall turned on? Configure the firewall or turn it off: http://www.limewire.com/english/content/firewalls.shtml

So which version of Panther are you using?

1st thing to try is to delete the LW Preferences folder called .limewire (whilst LW is closed!) & found here: /Users/your_username/Library/Preferences/LimeWire (BUT make a note of all your LW settings 1st, b/c after you delete the LW prefs folder you'll need to reset them.)

If still having problems than post back with details such as Fabion asked.