The error you used as the subject line would indicate an update problem. However, you state you have reisntalled OneCare, so that error would no longer apply if the install was successful.
What is the current state of OneCare, besides "at risk?"
Are there any "actions to take" when you open OneCare? Are you getting any error from OneCare when it starts? It could be as simple as needing to activate with your LiveID following the reinstall, or it could be that a service failed to start.
Note that you can contact support for help -
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve