Unused Port Blocking

I have Norton Internet Security 2010 installed on 2 laptops in my home.  They are both running Windows Vista 32-bit.  In the Norton History on one of them, it is constantly coming up with, “Unused port blocking has blocked communications.  Inbound TCP connection from 192.168.1.103, local service Port www-http(80).”  The port randomly changes to many different ports, not just 80 (for example, 81, 515, 2191, 443, and 9100.  The IP address it is pointing out is the other laptop.  I have performed a full system scan on both computers, and neither has come up with anything.  What could be causing this?  What should I do?  Are either of my computers at risk of something?