So you had been successfully using LW before that. From your details I can say the WRT54g is a trouble-some model with firmware problems. Do you run it port forwarded or in UPnP mode? I'm not too sure why that should affect LW starting up though unless, if in UPnP mode the failure to communicate with & from the router is causing problems with LW crashing.

You're using Java 1.6, do you have any other Java versions on your computer? If yes, I'd suggest removing them. I'm not sure about the present release Java 1.6 but certainly LW would not use the beta version 1.6 if other earlier java versions were on the computer.

Oh I just noticed your crash report. The problem seems to be with Java & it is at least trying to use Java 1.6. I'd suggest removing ALL java versions, rebooting, then reinstall Java 1.6 using the "Offline" installer so you're installing from your computer & not from over the net.

BTW AFAIK Java is used in the UPnP process.