I just found your post without an answer, following the forum migration of last night.Are you still having a problem a month later or was this resolved?
If you have not been able to activate OneCare, please contact support.
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90-steve