I had a problem with windows firewall so I decided to install Zone Alarm Free.
The problem was that it allowed visual basic listening a port (a visual basic application, not compiled, running from vb) It blocked it the first time only but later it was allowed even unchecking it or even removing it. Now I have ZA and I configured Visual Basic to ask for access and ask for server rights. Well, it asks for access when I made my application connect to a remote server, but it didn't ask when I made it listening to a port. I tested it connecting to localhost in Firefox and it receives data and ZA doesn't show any message.
Thank you for your time.