Time Machine couldn’t complete the backup to “TimeMachine”. An error occurred

Some WD drives have problems with Monterey and 12.1 did not fil all of them. See:

https://discussions.apple.com/thread/253298287?page=9

Also see:

last post

I just figured out a workaround on how to access my WD My Book after my Monterey update. Hope this helps! https://www.youtube.com/watch?v=oeAYiOe-_HM

Monterey is very sensitive to cable/drive connections. I would try another cable. I have seen this issue myself and changed the cable out to a fast certified cable to fix.

Now that you mention it as a related issue my TM drive would occasionally get ejected for no reason. After I removed turn display off (like sleep) I have not had any issue. I just use a screen saver.

Since the listserve is time sequential.... my post just now, refers to turning off the "Put disk to sleep" in "Energy Saver".

I also have an LG 5k display. After having my TM drive eject for no reason I finally took other's suggestions and turned off sleep function, use only screen saver and use energy saver to auto shut down my Mac at night and auto start in the morning. Now all works fine, no issues.

Could be problem with the WD disk

https://discussions.apple.com/thread/253298287?page=9

Do not use sleep either auto or manual for now.

Tbirdvet

Are things are simply flakey with Sleep on Monterey 12.3 running on an M1 2021 iMac?

I thought at first that my Time Machine failures were limited to when the displays were put asleep by the Energy Saver "Turn display off" option and were working when "Sleep" was invoked from the Apple menu. But then they started to fail on Sunday (always with being unable to backup a particular file, usually the "com.apple.LaunchSewrevices-3027-v2.csstore" file). I found a post saying (improbably) that Time Machine failures could be caused by having the Mission Control "Displays have separate Spaces" option unselected. (I have an LG UltraFine external monitor connected to the iMac.) Since I had disabled "Displays have separate Spaces" on Sunday before Time Machine backups started to fail after invoking "Sleep" from the Apple menu, I reenabled it on Monday. Now Time Machine backups often--but not always--fail when "Sleep" is invoked from the Apple menu.

Also, on Saturday and Sunday nights, after invoking "Sleep" from the logon screen, my iMac "was restarted because of a problem" while asleep during the night, and the Problem Report started with "Attempting to forcibly halt cpu 0". (In my 15 years with iMacs, I don't recall having an iMac restart by itself.) I found a couple of posts saying Mac restarts while asleep could be caused by having the Energy Saver "Wait for network access" option unselected. Since I had unselected this option on Saturday (thinking that might be related to the Time Machine failures), I tried reenabling the "Wake for network access" option on Monday evening, and the restart error did NOT occur Monday night.

I've been having this exact same problem on my 4-day-old M1 2021 iMac on Monterey 12.3. I first noticed it when the TM backup would fail when I had the display set to go to sleep after 10 minutes. I thought I had fixed it by checking "Prevent your Mac from automatically sleeping when the display is off" and UNchecking "Put hard disks to sleep when possible", "Wait for network access", and "Start up automatically after a power failure" under Energy Saver, and then using the "Sleep" option on the Appple menu.

That worked fine yesterday, but today the TM backups started failing again in "Sleep" mode from the Apple menu, each time on a selected file. (In my case, the only symptom is the "Time machine couldn't complete the backup" message and the TM backup will proceed once the iMac comes out of sleep mode.) I have a FireWire 800 hard drive formatted as APFS, connected with a Thunderbolt 3 to Thunderbolt 2 adapter and a Thunderbolt to FireWire Adapter. I guess I'll have to resort to just a screen saver as well.

I talked to Apple Support two days ago and they suggested re-installing Monterey on my 2-day-old iMac. They also asked for a video of the problem occurring.

The drive should be formatted APFS only. I would use Disk Utilities to erase and start over. You could also try the repair disc in Utilities and see if that shows anything.

Same issue. Time Machine not working properly after Monterey install. Apple engineer says the TM needs to delete lots of old backups to free up space for massive # of file changes due to new OS - while simultaneously trying to install new files. Literally 2 million changes needed to be made. It’s been 2 days. Still trying to finish initial backup. True hot mess. Apple needs to FIX this glitch.

This did the trick for me too. The file that failed before this fix was 6GB. I guess while it was processing the file the OS put the disk to sleep. Sheesh.

Amazingly, it solved my problem. Thank you!

MacOS acts like it "disconnects" the drive for TM, then Energy Saver puts it to sleep as it's not in use, the TM complains it can't find it..... Don't know if that is what happens, but that scenario is consistent.

Try it!

Using MacBook Air M1 2TB. I'm using a 2TB Seagate disk which was backing up fine until 12.2.1. Now backups do not complete, are glacially slow and Finder shows space used on the backup drive without any visible files. For example, if I backup 1TB of data from the computer, Finder shows 1TB remaining on the backup disk but no backup files are visible. Checked the drive using Disk Utility First Aid (no errors). Reformatted the disk APFS (case sensitive). Same result.