Have you tried using any other p2p apps & if so, do they give you the same problem?

Who is your ISP?

You could try changing to a higher port (eg something in the range 49152-65535). A higher port may not be blocked but LW is probably still going to pick up the NAT firewall within your modem. Does the modem support UPnP? If so, have you tried enabling UPnP & choosing that option within LW's options > advanced > firewall config?

Sorry, I can't help much more here. Someone else might have a better idea?