How did you subscribe? From within OneCare? Sign in with your LiveID at http://billing.microsoft.com and verify your subscription status. Consider reinstalling OneCare from http://onecare.live.com and activating with the same LiveID you verified at the Billing site.
If you continue to have problems, please contact support -
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve