Did your subscription expire on OneCare immediately upon updating to the 2.0 version? If so, unfortunately, you've encountered a bug that affects a small number of users during the upgrade. To resolve this you must uninstall OneCare, reinstall OneCare from http://onecare.live.com and activate the reinstalled copy with the LiveID you originally used to activate back in August. Before uninstalling, confirm your subscription LiveID by going to Help/About in OneCare and verify the subscription expiration of 8/08 at http://billing.microsoft.com *and* verify that your PC date and time are set correctly.
If you need help with this, please contact OneCare support.
How to reach support - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve