If you purchased a retail copy and need to renew with a key, do that by signing in at
https://billing.microsoft.com with your subscription LiveID, clicking on the OneCare subscription and then clicking renew, selecting the option to renew with a key.
If you have uninstalled OneCare and want to install again with a new suscription, then do not use the original subscription LiveID when activating.
If OneCare is installed and expired, and you went to the OneCare site and chose to purchase a new subscription online with a credit card and used a different LiveID, you need to remove OneCare from the PC and then reinstall from
http://onecare.live.com and activate/subscribe with the LiveID you purchased with.
-steve
Microsoft MVP Windows Live / Windows Live OneCare & Live Mesh Forum Moderator