Open OneCare, change settings, configure backup - uncheck the option to use backup. OneCare only knows about its own backup and has no clue about any external backup programs.
Also, 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
-steve
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