try this:
1. Run Cleanup Tool
http://download.microsoft.com/download/4/c/b/4cb845e7-1076-437b-852a-7842a8ab13c8/onecarecleanup.exe
2. Install on CleanBoot
Install Windows Onecare after restart
otherwise contact support
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2