The first thing to check is your PC date and time. The second thing to check, if that is indeed correct, is your actual subscription status. Open OneCare, click Help/About.... for the subscription ID. Log in with that subscription LiveID at http://billing.microsoft.com and verify your subscription status.
Once you've confirmed both of these and the site is correct, but OneCare on the PC is reporting that renewal is due, then contact support.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
And please report back what the solution was as many people have been reporting this problem, but rarely return to explain the cause or solution. (Wrong date, etc.)
-steve