Defender will be disabled by OneCare once it actually runs.
I suspect that your .Net Framework 2.0 is corrupt. Please try the following:
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 that works for you, please contact OneCare support.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve
