From: finkey on

Hey Mark, I had this too after changing one computer's connection from
wireless to ethernet connection, but found a fix. Mark your network
connection in your firewall as trusted on all the computers in your
network. Then, be sure all the computers on your network have the same
workgroup name. (Right click on My Computer, choose Properties,
Computer Name, then Workgroup) Then, step each computer through "Setup
a home or small office network" (go to control panel, network
connections) with the same workgroup name as well. Then restart the
computers. That did the job for us. Hope this helps.