If the G drive is your external drive used for backing up files using OneCare, you will need to manually delete or move files that are not part of the OneCare backup set or delete the existing backups and start over with a new Full Backup.
FAQ: How to Delete Backups
You may need to reset your backup plan after deleting the backups.
FAQ: How to reset backup plan settings (single PC)
I'm not clear on what this has to do with the Windows Live OneCare update you refer to, though.
-steve
Microsoft MVP Windows Live / Windows Live OneCare & Live Mesh Forum Moderator