I deleted one of your posts and merged your other two into one thread. There's no reason to start multiple threads.
If you are backing up to CD/DVD and this is happening to you, I suspect that there is either a problem with the brand disc you are using or the OneCare database is broken.
Personally, I'd be looking for an alternative to the OneCare backup since OneCare is at end of life.
See this post for End of Life information for Windows Live OneCare - http://social.microsoft.com/Forums/en-US/onecaregeneral/thread/81996436-edad-41ba-bdfc-02fc094e2ca9
You might try resetting the backup plan on the PC and also trying a new brand of disc: http://social.microsoft.com/Forums/en-US/onecarebackupandrestore/thread/5f18a60d-add4-4ff2-87cf-021db7e81917
If that does not work, please contact support:
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
-steve
~ Microsoft MVP Windows Live ~ Windows Live OneCare| Live Mesh|MS Security Essentials Forums Moderator ~