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

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".

Now I also got this issue. I have a time capsule. Worse, it happened two times within a week. If it continues to happen regularly, time machine is worthless. And that's too bad. One of the main reasons I have stayed with Mac rather than Windows is time machine. My wife lost important data because Windows has nothing like time machine, whereas in the past I have been saved several times by time machine.

I have a MacBook with a single USB-C port, which is used for an external screen. So, I can only do wireless backup. If Time Capsule does not work I'm screwed.

I reported the issue as a bug to Apple and they now sort of recognised it is a bug, but I don't think they've got a solution. Here is what they wrote to me:

"This is most likely a software issue and not a hardware issue with the Time Capsule. We’ve see an uptick of new reports since Sierra that we are actively investigating. We now believe the majority of these are due to a bug that manifests on systems using PowerNap but your case may be an exception. Since the diagnostic logs do not cover the time of the original corruption it is impossible to say exactly what happened.

There's really not a safe way to continue using the existing backup history. You can mount the sparsebundle and try copying any files you need off of it, but once it has been corrupted there is no way to repair it that does not also risk damaging the integrity of your backup history."

I strongly advise you to use another way of making your backups. What I did is two fold:

1) Use Carbon Copy Cloner to backup complete disks on a daily basis

2) Use Arq to create cumulative backups (like TM), in my case to Amazon Cloud Drive

Hope this is of help to you

"This is most likely a software issue and not a hardware issue with the Time Capsule. We’ve see an uptick of new reports since Sierra that we are actively investigating. We now believe the majority of these are due to a bug that manifests on systems using PowerNap but your case may be an exception. Since the diagnostic logs do not cover the time of the original corruption it is impossible to say exactly what happened.

There's really not a safe way to continue using the existing backup history. You can mount the sparsebundle and try copying any files you need off of it, but once it has been corrupted there is no way to repair it that does not also risk damaging the integrity of your backup history."

I received virtually the same message from Apple....but it was a few years ago. The only difference was that "Yosemite" was substituted for "Sierra" in the message.

Since this error was originally reported in "Snow Leopard".....Apple has been "investigating" this issue for quite awhile.

I have never had any problems with Time Machine backups when the backup drive is connected directly to my Mac via USB or FireWire. The corruption issue appears to be tied almost exclusively to "network" drives.

My wife has a recent iMac and is backing up to Time Machine on a Time Capsule via ethernet. I am using a late 2013 MacBook Pro and backing up to the same Time Machine via wi-fi. Since we both updated to the latest versions of Sierra, both of us are getting the above cited error message about Time Machine backups. I have been ignoring the warning and not creating a new backup. On my wife's iMac, Time Machine still appears to have last backed up on March 24, 2017. After a previous failure last October, she lost backup data for the prior year. On my MBP, Time Machine shows my last backup today. From what I have read, there is no independent way to manually verify the quality of any backup on a Time Machine disk. I am sorry I bought the Time Capsule and will probably purchase two separate small USB drives for backups. Time Machine is way overrated and there are no recovery options whatsoever.

I'm liking that "Sierra / Powernap" theory. I've got a house full of Macs, new and old, all backing up to Time Machine, and I've gone through all generations of Airport/Time Machine without ever before seeing this error, until this past January 2017, when it showed up for the first time on the newest MacBook Pro (Retina, 15-inch, Mid 2014), with PowerNap enabled. And now I've seen it 5 more times since then, including twice in the last two weeks, as of this morning. All only on that one Mac. The backup drive itself is only a year old, and I never find any errors or corruption with Apple's tools or DiskWarrior. So, in the meantime, I've disabled PowerNap and am now, yet again, creating a new "first backup." I'll leave PowerNap disabled and see if I can't at least make it to the end of the year without seeing this ****** message again!

Yes this happened to me a week ago and I let it rebuild. Now it has happened again. This is ridiculous: it is like having no short-term backup at all. Attempting to enter Time Machine just causes the screen resolution to change and garbage the screen, so no longer have any access to my backup.

Recommendations for an alternative backup hardware/software/protocol - ignoring Apple products - would be welcome.