I seem to have the same problem as everyone else. I have a Mac G4 with System 9.2.2. I connect via Cox cable (cox.net), a high speed cable modem. I use a Linksys router. This setup worked fine with the previous versions of Limewire.
I have today just installed 2.5.5 over version 2.4.3 which until now was working perfectly. No other changes to my system. This version apparently refuses to connect, button at left-bottom remains red. And unfortunately, I have erased my previous version (so confident was I!).