That's not something that Windows Live OneCare is designed to address. That error typically means that there are startup programs being called that are invalid due to incorrect removal. This can happen in some cases when malware is removed by an antivirus program. If this began after OneCare removed a threat, please contact support.
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
If not, then start here for resources for XP issues:
XP Solution Center - http://support.microsoft.com/ph/1173#tab2
-steve
Microsoft MVP Windows Live / Windows Live OneCare, Live Mesh, & MS Security Essentials Forums Moderator