Try this first:
OneCare won't start - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2523777&SiteID=2
If that doesn't work, then this problem may be caused by a corrupt .Net Framework 2.0.
To repair .Net Framework 2.0 on XP:
Open Control Panel
Select Add or Remove Programs
Locate Microsoft .Net Framework 2.0
Select the entry and when the installer launches, select Repair.
Reboot when it completes.
Alternatively, see this KB article:
http://support.microsoft.com/kb/306160
To remove a corrupt .Net Framework install, use this tool:
http://astebner.sts.winisp.net/Tools/dotnetfx_cleanup_tool.zip
The download of .Net Framework 2.0 can be found here:
http://www.microsoft.com/downloads/details.aspx?familyid=0856eacb-4362-4b0d-8edd-aab15c5e04f5&displaylang=en
To repair .Net Framework 2.0 and 3.0 on Vista, see this blog entry:
http://blogs.msdn.com/astebner/archive/2007/03/26/how-to-repair-the-net-framework-2-0-and-3-0-on-windows-vista.aspx
If none of the above resolve the issue, consider uninstalling and reinstalling OneCare. Note that you will need to activate OneCare with the same LiveID you originally subscribed with and all previously stored settings, including backup configuration, will be lost.
If you are still unable to resolve the problem, please contact OneCare support:
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve
