Try running the One Care install cleanup tool - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/399071e2-49dc-4767-932d-d261e3965943 then install One Care. If this does not resolve the issue please contact support. How to reach support - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90