If the router supports UPnP, make sure it's enabled & then choose the UPnP option within LW's tools > options > advanced > firewall config.

If that doesn't work, you could port forward. Go to the site below & see if your router's listed. There's a lot of ZyXEL routers there, might help you to work out which one you have. Once you've found your router, choose LW from the list of programs & follow the instructions from there. If setting up a static IP is part of the instructions, don't miss that step!!
Remember, LW's listening port & the port forwarded must be the same number.

http://www.portforward.com/english/r...outerindex.htm