Two of my clients in the space of one week have had their OneCare effectivly shut down. Firewall is blocking use of local computers. I tried the MS Onecare Firewall repaif and it didn't fix the issue. Had to run the OneCare Cleanup and reinstall. One client is irate! Virtually shut down his business for several hours while re-installing on 10 PC's! This is not satisfactory.
I can't tell you why you would need to reinstall as the repair tool should resolve the problem in most cases when the update has been applied and the firewall fails to start. I'm sorry about the irate customer and sorry that you had to deal with the problem. :-(