Hi, Phil. Is the backup configured as a Centralized Backup from a hub computer? If so, it would need to have permissions for all Users to have full rights to the Shared location. If it is only a single PC with an external drive, and since you've done an update of the OS to Vista, it may be worthwhile resetting your backup. Try the following:
Open OneCare
Click Change Settings
backup tab
Click change settings in the lower left
Make sure that the first screen for Centralized Backup has "No Centralized backup" selected
Click your PC on the left.
Uncheck the selection for "Turn on backup for this PC."
Click Next and save the revised plan.
Go back to the backup tab and click Change Settings in the lower left once again.
Select your PC and click.
Click Turn on backup
Select the change location link and select the drive you want to use for backup
Modify the schedule as desired for "When"
Select the file types as desired for "What"
Click next and save the revised plan with the new selection.
If that works, and then after doing a new backup, go ahead and delete the old backups - which is another pain, unfortunately.
http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=1698096&SiteID=2
-steve
