The right click option is an Explorer extension - a shell extension. If it does not appear, and you've checked by right clicking various folders and files and drives in Windows Explorer, then I suggest reinstalling OneCare.
Or, you can 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 ~