Did you activate the subscription with a LiveID by clicking Subscribe within OneCare? Is it a new install or is it simply reporting an incorrect expiration?
If it is the latter,
If your subscription is correctly shown at the Billing site, but incorrect in OneCare and your PC date and time are correct, please contact support.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve