Time machine backup failing since update

I had this issue as well and I think I have it resolved. I chatted with apple support for a while, and at first it seemed like the only solution was formatting the entire drive, but I have multiple partitions which I couldn't format on the drive. The solution seems to be to reselect the disk as a backup and encrypt it. Support asked me if I had FileVault on, which I do, so I'd say first ensure you have FileVault enabled (System Preferences > Security & Privacy > FileVault). Next, go into Time Machine preferences (System Preferences > Time Machine), navigate to "Select Disk..." and you should see your time machine disk under "Backup Disks" as well as "Available Disks." Select the Time Machine disk under "Available Disks" and make sure to check the box next to "Encrypt Backup" before clicking "Use Disk." It then prompts you to choose a password, and then it will Encrypt the disk. Time Machine is now preparing the backup, so this seems to have worked. I will update if this fails, but as of now, this is my solution.

I also got this error. So I read this unhelpful thread below from people stating this "can't happen", and I remounted my external drive that I backup on, and then clicked SELECT DISK, and reselected my backup drive (the same drive) and it worked!

Hope this is actually helpful to others.

Good luck.

I was having the same "encryption" problem. Open time machine preferences (had to do it twice to work), choose select disk, selected my external HDD and clicked backup now. It worked.

Good luck,

Nelson

That message is really odd, but I strongly suspect it's not accurate. An encrypted backup simply cannot spontaneously become unencrypted, otherwise what good is encryption? It makes no sense. It's far more likely the backup is corrupted, leading to an erroneous interpretation of its encryption status.

I wouldn't rely upon that backup.

wzinet wrote:

As a side note, I'm using an AirPort Extreme for the backup disk.

Assuming you mean a USB hard disk drive connected to an AEBS I'd just get a new one. Not only is one and only one backup less than ideal, the most likely cause for your problems is simple, mundane, hard disk drive failure.

The other one will still retain its backup history should you need it, assuming it's intact, and suspect it isn't. Erase it when you're reasonably certain you no longer require it, but the disk itself is probably no good.

Got the same message: Time Machine did not back up because the backup disk was previously encrypted but is no longer encrypted. I reselected the disk and it started backing up but says it's no longer encrypted. C'mon Apple. Get your act together!

Try removing the backup disk from Time Machine, then re-add it. See if it will continue the backups.

Did you decrypt the backup drive?

Same thing here with an update to 10.13.6. Last backup worked approximately 30 minutes before security update 2019-004 (10.13.6).

I'm using a Time Capsule. I don't think that the disk itself is encrypted in a time capsule, I believe the backup disk image is individually encrypted. Either way, I obviously did not change that.

Removing the disk and re-adding just gives this:

---

The disk “Backup 1” already contains an unencrypted backup for this computer.

Would you like to continue using the existing unencrypted backup, erase the existing backup and start a new encrypted backup, or choose a different disk?

---

Weird. I guess it's possible that a previous version of macos incorrectly created non-encrypted backups but somehow labelled them as encrypted and now this version is correcting that mistake. Doesn't really matter I guess, there's a problem somewhere.

Not so hot Apple! Backups are one of the key features that have to be 100% rock-solid.

I just started having this problem, too. It seems too coincidental that both our hard disks would suddenly have issues/go bad after updating. I suspect something else is wrong relating to this update.

Same problem here, the Time Machine sparse bundle disk image was encrypted and now it's no longer encrypted.

I tested it and I don't need a pasword anymore to acces it even from a foreign computer!

This shouldn't be possible! It seems not safe to make copies of all your data on a Time Capsule..

I'm suddenly having this bug as well.

• I've never encrypted my boot drive nor my backup volume, and frankly I'm definitely not encrypting a 17TB RAID 5 NAS to solve the problem, that would take a month, not to mention it would take weeks to start that backup from scratch.

[Edited by Moderator]

i figured i’d just bite the bullet and get it done. it took about 27 hours for my 4tb drive to encrypt. oddly enough, when i used the drive the next day, it said encrypting again, back at 68% completion, but i was able to eject the drive before it reached 100%.

Thank you for putting up a solution in non-tech language, with instructions that I could easily follow. 22 hours to go on the encryption thing, but back up now preparing.

I am 'in charge' of home tech support and mac back ups for my partner, on the basis that I am slightly more tech-savvy than she is - but I'm still just a home user who gets confused by the level of detail on some of these posts! It's great to have been able to fix this within 20 minutes of discovering the problem.

So thank you!