Lost a backup set

I'm running Norton 360 on a win-8 machine.  I recently had to reload Norton and now a backup set on an external computer is not showing up it the backup list--only default set (on-line) is showing.

 

Following a thread, I ran Arestore.exe.  Not in list.  Then I reset, but it was still not in the list.  Any other ideas other than reformatting the external drive and setting up a new backup set?