This error typically occurs if you are trying to install Windows Live OneCare to an older operating system such as Windows 98 or Windows 2000. Windows Live OneCare can only be installed on XP SP2 (32 bit) or Vista.
If you are using a support operating system and encountering this error, please contact support.
How to reach support - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve