Then, reinstall OneCare from http://onecare.live.com and activate (subscribe) from within OneCare, signing in with the subscription LiveID (found under Help/About... in OneCare on the other PC)
Then, reinstall OneCare from http://onecare.live.com and activate (subscribe) from within OneCare, signing in with the subscription LiveID (found under Help/About... in OneCare on the other PC)