If you reinstalled OneCare or installed OneCare on another PC, you need to activate OneCare. It appears, based on the message that your "trial" has expired, that you did not activate OneCare with your subscription LiveID.
If you don't recall the LiveID you used for your subscription, you will need to contact support who can provide that information to you using your Key and/or contact information.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
Alternatively, sign in at http://billing.microsoft.com with email addresses that you have set up as LiveIDs and one will show your subscription listed - that would the LiveID to use to activate.
-steve