Reset your backup plan per the instructions here:
http://social.microsoft.com/Forums/en-US/onecarebackupandrestore/thread/5f18a60d-add4-4ff2-87cf-021db7e81917This will allow you to point to the new drive and start a new full backup.
-steve
Microsoft MVP Windows Live / Windows Live OneCare, Live Mesh, & MS Security Essentials Forums Moderator