Time Machine backup failed. Why?

[space-time]

Sarcany wrote:
Happens when there's a network-interruption during a backup and often corrupts the target image.

Yes, reboot the NAS to clear the "busy" flag on the image.

Follow Up Question.

Is the target image still corrupted? Should I worry about that?

What happens if my MBP is backing up (via WiFi) to NAS and I close the lid, MBP goes to sleep. Does NAS close the target image? or it stays open until I wake up the MBP?