1. See
Configuring Norton Internet Security
2. If you're using XP then also see this about your xp firewall:
http://www.limewire.com/english/content/firewalls.shtml
3. See if
Fixes for Limewire can fix the problem for you.
Can you give us a total desciption of your set up: 1. OS version, 2. What firewalls you have, 3. ram, 4. HDD space available, 5. Connection type, 6. Modem & router brand name & model numbers, 7. Where are you trying to connect from (home, school, work, etc.)?