Fw: How To Delete A Vista Backup Set? - Vista Forums

This post solved my problem!

Mark L. Ferguson:

...
Open the location where the backup is saved.

For example, if you backed up your files to an external hard disk labeled
"E," connect the external hard disk to your computer, and then open drive E.

Right-click the folder containing the backup you want to delete, and then
click Delete.

Notes
Backups are saved in this format: \\Backup
Set . For example, if your computer name is Computer,
your backup location is E, and you backed up on April 2, 2006 at 16:32:00,
that backup would be located in E:\Computer\Backup Set 2006-02-04 163200.
You would right-click the folder named Backup Set 2006-02-04 163200 to
delete that backup.

When you make a full backup, a backup folder is created and labeled with the
date for that day. As you add updates, that date stays the same, but your
backup is not out of date. The next time you make a full backup, a new
backup folder is created and labeled with the date for that day, and any
updates are then added to that new folder. You should not delete the current
backup folder.

How To Delete A Vista Backup Set? - Vista Forums