When you do a backup, the software first runs a “Repair & Compact” to check that the data you’re backing up is OK and not corrupt. If your file is corrupt, then the “Repair & Compact” process will fail and the backup will not take place. This is to prevent you from potentially overwriting a good backup with a corrupt one.
If this is happening, see the next question below to try and fix the corrupted file.
Note: If the “Repair & Compact” process is completing successfully but the backup still fails, then we would recommend that you try backing up to a different device as your backup device may be faulty.