Time Machine suddenly thinks source is encrypted

I’ve got a very strange situation that cropped up 36 hours ago. I’ve been backing up my laptop via Time Machine to an external drive attached to an iMac, the iMac being used as a server. Everything was set up per instructions in Joe Kissell’s Take Control Of Backing Up Your Mac, and it’s all been working well for years. Two nights ago, though, the laptop hard crashed waking from sleep, and since then Time Machine hasn’t been able to back up.

Backup will start, and then while it’s preparing I’ll get a straight-out incorrect warning that I’m attempting to back up an encrypted disc to an unencrypted one:

The laptop’s never been encrypted, though; I’ve never touched FileVault. I double-checked, afraid that the hard crash had corrupted something, but according to System Preferences I’m still unencrypted:

Shortly after that, the backup will just stop, without any further error message. Time Machine preferences will just say that the last backup was two nights ago, and the next backup will begin in an hour. If I wait 'til then, or try to force a backup now, the same thing happens again.

Anyone else ever see this? I’ve tried restarting both the laptop and the iMac, I’ve double-checked the Sharing preferences on the drive that’s being backed up to, and I’ve deselected and reselected the backup drive in TM preferences, but I can’t get Time Machine to back up any more.

Annoyingly, this all happened just before I upgraded the OS on the laptop (Mojave → Catalina, an upgrade I’ve been putting off for an unreasonably long time, and it took me quite a while to figure out workarounds for all the 32 bit apps, including the 25 years of email archives locked up in PowerMail). I’ve got a bootable duplicate of the laptop on a separate SSD, but now I’m loathe to upgrade when my Time Machine backups seem to be on the fritz.

Have you checked the laptop’s drive with First Aid in Disk Utility?

Yes, as part of the prep work for the now-on-hold OS upgrade. Comes out with flying colors.

Really stumped. It’s continuing to fail to update every hour without any error message - it seems like the warning about encryption only happened after I deselected and then reselected the target drive, which makes sense as a trigger, even if the message is wrong about the source being encrypted.

Sigh. Further information: in the course of further jiggery & pokery with Time Machine & Sharing, I think I can now confirm that the erroneous error message about encryption is triggered every time I re-select the target drive. However, I’m now getting an unhelpful error message stating the target disk “does not support the required capabilities”:

I’ve double-checked all settings in the File Sharing setup on the target iMac, and even deleted the shared disc from File Sharing and set it up anew. When I then select the target disc in Time Machine preferences on the source laptop, it correctly asks for login credentials on the target, and all of that goes through correctly, so it’s able to connect to the networked backup disc. But it will continue to fail to back up, once an hour, until a few hours later it will again give the above error message.

It’s not like there’s a good time for automated backup to just mysteriously stop working, but if there was, “just before you upgrade to a new OS” would be a likely candidate.

This strikes me as the kind of problem that Disk Warrior is really good at solving. Over the years I’ve had a lot of good luck pointing Disk Warrior at problems that Disk Utility either didn’t acknowledge or was unable to fix. If you have Disk Warrior or can get access to a copy, I would recommend running Disk Warrior on both the laptop disk and the Time Machine disk.

automated backup to just mysteriously stop working

Seriously…don’t use TM to a network location for a couple reasons. First is you get a .dmg instead of direct files and folders. Second…it simply doesn’t work reliably and hasn’t for probably 3 major macOS releases. I’ve e mucked about with it for hours…and having done macOS since the System 5 or so days I’m pretty well versed. Two laptops setup to alternate TM to an Intel and AS Mac…identical settings, shares, perms, etc. Yhey both work, then backup of laptop A to machine C fails for awhile…sometimes with the ‘start over’ message but usually with just ‘it ain’t working’. Then it fixes itself until one or the other laptops fails again…no consistency between source and destination and problem.

Get a copy of CarbonCopyCloner and use it instead with SafetyNet on…provides same capabilities as TM, Finder readable destination…and best of all it just works. Instead of mounting the destination and using Choose Folder…select Remote Macintosh since that works more reliably if the laptop is asleep. It just works…bulletproof.

TM to a locally connected drive still works fine except for the random ‘start over’ thing…but laptops are less conducive to always connected externals than desktops. I still enable TM on them to a drive that’s never connected again for months anyway…that way it does local TM which is not good backup of course but let’s you more easily get the version of the file you wrote over 3 hours ago. And I set my CCC jobs to just be daily instead of hourly but you can set whatever periodicity you wants.

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Well, a less-than-illuminating followup. I continued to not be able to back up to the external drive shared from an iMac. I was under some time pressure, though, because my laptop’s still on High Sierra, and my tax software (H&R Block) won’t run under anything older than Catalina. So I took the quick, cheap, and ill-advised route of buying a Western Digital My Cloud Home, a single-drive NAS that I can just plug into my router, that advertises Time Machine compatibility. It was easy to set up, and most importantly I could just pick one up at a Best Buy two miles away from home, with an hour to spare before a snowstorm made the roads problematic for a good 18 hours.

Somewhat to my surprise, given the reviews of WD’s My Home Cloud, it worked as advertised, albeit dog slow - first backup from the laptop took four or five days (1.5 TB of data). I’ve still got the original iMac-hosted.sparsebundle targeted in TM preferences, in addition to the new WD-hosted one, so periodically over that span of time Time Machine would also try to back up to the old share, but it continued to silently fail.

Cut to today, when I had cleared out enough of the 32-bit cruft I had on the laptop that I could finally update to Catalina (I’ll upgrade further once I get taxes done). Everything seems to have gone smoothly, I’ve taken care of the obligatory blizzard of security notices as I launch apps, and now suddenly…Time Machine has decided it can back up to the old share. No idea why, but I guess I’m glad the WD networked drive was less than $200.

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