Not a reply to the OP, but a similar problem
I have a 3yr old 12" PB, running latest version of Tiger. No problem whatsoever with this computer.
I signed up for the Mobile Me trial. Now I get this message whenever I go to the network settings menu. While I connect both at home and work with no problem, I am now not able to change any network settings (should I want to) as the this screen does not allow me to do anything. Even when I click the "OK" button, ot just keeps coming back.
The only way out of this screen is to Force Quit SysPref.
The other thing I notice is that I am not able to "eject" the Network, something I could always do in the past.
Any suggestions would be welcome.