I moved your post out of the Off Topic folder where it was in danger of being overlooked.
Knowing the error message would be helpful....
Try logging into http://billing.microsoft.com with the LiveID for your subscription (Help/About... in OneCare, the Subscription ID is your LiveID).
If you still encounter an error, please contact support for help.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve