When viewing backup history, you might see backup failures or warnings. Backup failures indicate the backup did not run, or that it ran but failed to back up more than one in one-thousand files. A backup warning indicates the backup ran and completed, backing up more than 99.9% of all files, but less than 100%.
When you see a backup failure or warning, you should investigate the reason for the backup status. View the Backups Report for details of a failure or warning. Click on a backup in the Backups Report to view information regarding that backup. This window shows the raw output of any failure or warning messages that the system generated. These messages provide a good indication of why a backup failed, or completed but had warnings. View the Failures Report for details of the backup failure.