Any idea why I would be seeing this? It was just an incremental backup after the initial backup had completed.
00:25:21 : A fatal error occured: The backup is having trouble uploading files to Dropbox, it has failed 10 times and is aborting the backup.
00:25:21 : Approximately 7% complete.
00:25:21 : Error uploading 'mysite.com/wp-content/backups/mysite-backup-core.sql' to Dropbox: Forbidden. Your app is making too many requests and is being rate limited. 503s can trigger on a per-app or per-user basis.