OneCare does not scan or clean the registry. You'll find many discussions on that topic here. My opinion is that registry cleaning is dangerous and mostly useless.
For your backup issue, it is possible that something is conflicting with OneCare's backup component. This can be packet writing software that often gets installed and activated by default with CD/DVD Burning suites. InCd and DirectCD are two common ones that come with Nero and Roxio, respectively. Uninstall these and the problem may go away. Otherise, please contact support for help in resolving it.
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 Forum Moderator
