Hmmm .. the reason why I asked you specifically about Norton is due to the fact that the Norton files and registry entries if left on the computer can cause such behaviour..... the mention of 2 computers out of 4 was the one that made me think in that line...
more over the new version has lots of other technical changes that can cause issues if there are traces of Norton found
In a similiar case...
I found some applications from Symantec on
c:\program files\common files\symantec shared\
again.....
see if running This
helps.