well, I figured it out. The router has a bunch of computers linked by ethernet cables but I added an Apple Airport Express Base Station for access by portable Mac. The DHCP is turned off in the base station and so is the firewall, plus the Macs that failed to connect were connected to the router by ethernet cables. Since I wasn't going through the base station, I assumed that it wouldn't be an issue. If I turn off the airport, then LW works. This wasted a lot of time figuring out so perhaps this will be of use to someone else?