Time Machine completed a verification of your backups. To improve reliability, Time Machine must create a new backup for you.

I encountered this problem after upgrading to Sierra, like most people commenting here.

It recurs every two months or so. My Airport firmware is up to date, and I have no other network related problems.

For my setup, at least, I've finally solved it.

I have 4 different machines backing up to same TC.

No problems for several years, then began to have troubles with 10.11 and persisted into Sierra

Only one iMac would get this error message, the other 3 were fine.

I even tried reformatting the HD in the Time Capsule with no improvement.

I then did clean reinstall of Sierra on the involved computer, now no problem for a month and counting!

After the clean OS install, all other programs were clean installed also, minus ClamX.

It seems that the ClamX Sentry may have been the culprit.

pjleeson wrote:

It seems that the ClamX Sentry may have been the culprit.

Interesting conclusion, but one that nobody else has reported. It would be helpful if you could verify this and then report it by opening a ClamXav help desk ticket. Provide as much detail as you can as well as link to this lengthy discussion. I suspect you will be asked to run the built-in diagnostics in order to gather complete information on your setup.

You can always remove it after, if necessary, by dragging the application to the Trash Can and within a few seconds you'll get an alert offering to remove the remainder of the installation.

I have this problem too and do not have ClamX so I don't think it has anything to with it. Probably reinstalling got rid of something that was causing the problem, or you will get it again in due time

I just got this message on a late-2013 13" MacBook Pro Retina backing up to a 2TB Air Capsule. Didn't know what to do so it's now doing the painfully slow new backup.

But: What is the worst thing an automated backup program can do? Destroy all your backups without offering any recovery option, in the name of "to improve reliability". And that's what this program does. Get to work on this Apple. It's not like the Time Capsule is cheap. Earn your margins with reliability and functionality!

Hi James,

I reported this as a bug to Apple and they seem to be working on it, since they have asked for diagnostic info and sysdiagnose data. Until it has been solved, I turned off my TC because I don't want to lose my backup. In the meantime I backup using Carbon Copy Cloner and Arq (cloud backup)

they seem to be working on it

You might not be aware that they have been telling users that they have been "working on it" since the bug first appeared in Snow Leopard (10.6.4) in mid 2010, so it may yet be awhile before a solution is offered.

ha, ha

They either don't understand it, or don't want to fix it. It's been years.

It really is one of those 2 possibilities

I use Carbon Copy because I can't count on Apple to reliably do a backup. Sad.

I have had this problem only with the Airport TC. It seems that if I send the Time Machine backup to another external hard drive, there's no problem.

I wonder if anyone can corroborate that experience?

I'm certainly aware of that, given the number of reports about this. Let me phrase it like this: there has been a certain activity on Apple's side since I filed a bug report about this. We'll just have to wait and see if anything comes out of it.

I don't think Apple will ever look at internet fora to search for problems users report there, so the use of these kind of fora is i.m.h.o. more in finding if you're the only one with a certain problem, finding work arounds, possibly discovered by others. Ultimately filing a bug report at least gets the problem to where it belongs: with Apple

It is nearly 5 years later, and I too am now experiencing this problem. Ugh.

FWIW I accidentally unlinked my NAS Time Machine drive a few months ago and had to relink it using 'tmutil' in the Terminal. It was a pain in the arse. But I got it to work and all was well...

For about three months, and then today bam, I got this message verbatim to yours.

I can only assume that this is related to my unlinking and relinking the drive, though I can't for the life of me imagine why it would have taken three months to "complete verification" (using 1000mbps ethernet).

Oh well, I'm 99% sure I don't need anything on the backup. But that 1% though!

Just spent 1 hour and 20 minutes until the third specialist told me (paraphrasing) "Oh yeah, we know all about this problem with Sierra and Airport Time Capsule back ups - I assure you that we are working hard to fix it, it is one of our highest priorities and I will let you know right away when it is fixed". Not sure if that is any consolation for the 19 pages of discussion over the past five years, but there you go.

Also, they told me to archive a copy of the backup so that it won't get overwritten and that if you back up to an external USB drive instead of the Airport Time Capsule there don't seem to be any problems.

Thanks, Boston Mac User!

I too have found that backing up to the USB drive is trouble free, so I guess I will go back to that for now.

I was surprised that Time Machine does in fact overwrite everything when it starts over. How does one archive a copy of the backup on the TC drive?

Go into the time machine disk through Finder and just rename the existing back up before you let time machine overwrite it. Then the next back up will be written to a new file. You may get a prompt the first time that tells you the "disk has changed" and you can just click "use this disk".