error with backup settings

I have my backups scheduled for 7PM every Sunday. Files are saved to my Drobo 5N. I've seen this error but my backups are working properly. I clicked on the Drobo, clicked next and checked my settings, which were correct and saved them. It says my last backup failed but in the first picture it shows that a backup was made on the 3rd.

I did enter my user name and password for the Drobo when I first setup Backup and Restore.
I have a flag in the notification center telling me to "back up your files". Why is this? I have backup set to run automatically.

(pictures are out of order)

I clicked on run backup now and it did backup my computer. Not sure what the issue is.

Hi Havoc,
Is your format on the Drobo NTFS, first FULL backup will complete on Fat32, but sebsequent scheduled backups tend to fail, "apparently" due to lack of space.

Roy

The format is what ever the default Drobo format is. I have almost 10 TB of storage with the Drobo.

The backup ran today, in the background, and I didn't experience any errors. I don't know why the action center was showing me an error earlier.