An item with the same key has already been added Thanks, Chris.
I did hear back from support overnight, and they suggested running a full backup as well, but I may have found another work-a-round.
On the backup client on the local system, select 'Options' and 'Tools'. On the 'Repository' tab, click 'Synchronize Repository' and 'Synchronize Now'. So far, that has seemed to work on (2) systems.
I have another dozen or so backups that failed overnight. I'll report back if I find any more info.
Regards,
Stephen