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

As using a NAS is not supported.......

Apple does not agree with you. You might want to review this Apple Support document:

Backup disks you can use with Time Machine - Apple Support

Time Machine can back up the data on your Mac to these backup disks:

• An external USB, Thunderbolt, or FireWire drive connected to your Mac
• An AirPort Time Capsule's built-in drive (any model)
• An external USB drive connected to an AirPort Time Capsule (any model) or AirPort Extreme (802.11ac model only)
• Network volumes connected using Apple File Protocol (AFP)

Unfortunately though, any kind of network drive.....including the Time Capsule.....is more susceptible to corruption issues than a USB drive connected directly to the Mac.

I have received the second Time-Machine failure in the past 5 months. Using MBP Late 2013 with 15 inch display and Sierra 10.12.5 (just updated Sierra prior to failure), backing up to a 3TB Time Capsule. I have Power Nap enabled and haven't tried turning it off. Following this chain for a couple of months and not clear from responses whether or not that is a real or imagined cause.

When I got this notice I checked the Time Machine icon on the menu bar and it still showed that the previous backup was being verified. That disappeared when I selected 'back up later.' The later attempt to backup results in re-appearance of the message below.

I don't understand other commenter's mentioning running Disk Utility, as the Time Capsule networked drive does no appear there. I recall from previous research that the Time Capsule backup drive cannot be fixed using Disk Utility. Perhaps third-party drives can be.

I tried to follow link to Apple Bug Reporter from dinky2 above, but takes me to an Apple Developer login page where my Apple ID is rejected. I wouldn't mind barraging Apple about this problem but where is the best place to do that?

I suggest everybody having this problem issues a bug report to Apple Bug Reporter

Maybe flooding them with the same message will eventually get them to take some serious action. This problem has been around for years, looking at the numerous reports on the internet. They just don't do anything about it. Apple just won't take the trouble to look at any fora

Apple rarely responds to anything posted in this forum. It's user to user.

This discussion started over four years ago, so the only users that might see it are those who posted here and are still following it (I have no idea why I still am).

See C13. " . . . Time Machine must create a new backup for you." and if that doesn't help, start a new topic.

Thought I would share my issue.

Had a early 2009 24 inch Imac. Linked to time capsule, backups without any issues.

Bought a new Imac , 27inch, 2TB on Dec. 26. Started up machine, it was fine. Downloaded data from time capsule, everything downloaded, good to go. This new machine had El Capitan. It seemed to be doing fine. Then I upgraded to Sierra, and soon after (within a day), started getting prompts about how backups couldnt be completed, if issue continued go to disk utility, and run first aid, and then ultimately recieved the message "Time machine completed a verification.....", just like other posters here.

I contacted apple care, long story short, they had me erase all my data (3 years ) from time capsule and start backing up again.(I did have data stored on a seperate hard drive as well, just in case) Did that, took several hours, and next day, the same thing started happening again.

The interesting thing is that I also have a macbook pro, using El Capitan, and it downloads backups to the same time capsule, without any problems!

Called apple care again, and long story short, they decided it was a problem with the OS (sierra), and did clean installs, resets, etc, and still no success. Ultimately they had me totally erase the hard drive, and at that point they kinda suggested to exchange the new computer for another new one. Apple store is only 5 minutes away for me.

Got a another brand new 27 inch Imac, 2 tb, and was able to get my information on it from the hard drive. This one already had Sierra on it. And soon after that, several issues popped up on trying to backups. First issue was that there was keychain issue(I never use keychain, which also had my email hosed up), some how that issue finally went away, and then the "Time machine completed a verification"......started again.

At that point, I connected another external hard drive and am having backups downloaded to it using time machine. Works perfectly, and at the same time, the Macbook pro is still downloading backups to the time capsule without any issues.

I probably have invested 5 hours with apple care in this, and still no resolution. Guess I will just have to use my workaround. Maybe a future upgrade of Sierra will fix it. At this point, I have no clue on what to proceed on.

I have "solved" this problem a number of times, only to have it come back a week to a month later. I had seen it a few times in the past, but it became a regular occurrence only after I upgraded to Sierra. Until a week or so it was only happening with one of two Time Capsules that we have in the house, but now it has happened with the second one as well. There are other symptoms as well, such as the network machine name on my MacBook changing periodically due to a "duplicate" on the LAN, and various Apple devices disappearing and later reappearing in the Airport Utility. I believe all of these symptoms have been described by others here as well.

Yesterday I installed an old Airport Extreme router between our AT&T Pace DSL modem/router and our LAN to see if that would help, configuring the AT&T box to pass its IP address and traffic through to the Airport Extreme ("DMZplus") to avoid "router behind router" and other issues. All is working as expected, although I realize that that does not mean that the problem is "fixed." While the Airport Extreme is an old model from about 2009, it updated to the latest firmware when reinstalled. For good measure, I also switched from using a non-Apple wireless access point to using our late-model Time Capsule, and I replaced an "iffy" Ethernet cable (it was two shorter cables joined with a coupler) connecting the Apple TV to the LAN with a better quality one.

While I was testing the new configuration, I noticed that my MacBook Pro was frequently losing its LAN connection. I have seen this problem before, and it seemed to be worse after LAN reconfiguration, but it did not appear to be related to the router. At first I thought it might be my unmanaged gigabit switch, which feeds wired Ethernet jacks throughout the house, but then it occurred to me to swap out the (external) Thunderbolt Ethernet adapter on my Mac for my spare. That seems to have fixed the disconnect problem!

Now it seems as though there may have been another explanation for the corruption of my Time Capsule backups, which only happened to my Mac and not another one located elsewhere in the house. It may be an issue of lack of robust error recovery on the part of Time Machine, possibly exacerbated by changes made to the network support (or in Time Machine itself) in Sierra. I believe this was mentioned as a possibility earlier in this thread, and I believe that it is quite possible that it explains what I have been seeing. Time (Machine) will tell...

Can anyone tell me why?

Your backups are corrupted.

I am afraid to start a new back up if I have to erase everything first.

Then, you can copy all of the data on the Time Capsule to a USB drive before you click to start a new backup. But....because the backups are corrupted, they will be of no use to you.

Using Sierra? Apparently you need to regularly back up the backup and restore it every time Time Machine corrupts it, or find other backup software besides Time Machine. Or figure out what in your local network might be "causing" the corruption.

My guess is that Sierra is somehow lacking in its network error recovery, but I really don't know. We have two MacBook Pros in our home network (which is now using a brand new Airport Express for its router), and each one "developed" the problem when Sierra was introduced. Actually, the second one is a brand new MacBook Pro that came with Sierra installed. It replaced an older Macbook that never, ever encountered this problem in our network. The other is a mid-2015 MacBook Pro that did not run into this issue until upgrading to Sierra. Time Machine currently fails every few days, although the frequency has varied over time since installing Sierra.

No doubt. But since OS versions prior to Sierra did not require a "perfect" home network to function, and many home networks are less than perfect, and Sierra doesn't provide any user-level tools of which I am aware to diagnose such "imperfections", and since Apple has been removing diagnostic capabilities from its network devices, I can't help but feel that Apple should be addressing this issue, even if it only shows up in a minority of networks.

The most likely suspect in my network is the external Apple Thunderbolt Ethernet adapter that I have to use with my MacBook Pro, which is a recent model that no longer contains an internal adapter. It is unreliable, and I noticed that Apple also seems to have ceased to sell them, relying on other vendors instead. The adapter that I used for the first year or so failed outright, and I am using a spare that I bought at the same time. Just now it is showing the first visible symptoms of developing an intermittent connection, after a couple of months of use, and presumably it will also fail outright within another year. I am considering going to a USB Ethernet adapter, because it has a more solid connector (USB instead of Thunderbolt) and it doesn't place the RJ-45 connector inline & close to the Mac, where it is bound to cause problems.

If that is the case, it would seem that "my" problem is Apple's problematic hardware. Under those circumstances, I would still very much appreciate it if Sierra TIme Machine would do proper error recovery in my imperfect network, the way earlier versions did, even when confronted with a poorly-designed Apple Ethernet adapter.

If that is not the case then nearly all of the rest of our home network is Apple devices as well, and my feelings remain the same.

For me, it started when I upgraded my MacBook Pro to Sierra. Another, older MacBook on the same network but not on Sierra (and used by someone else) was unaffected. When the other Mac was replaced with a new MacBook Pro pre-installed with Sierra, it developed this same problem.

Up until now I have assumed that this is environmental, since most Sierra users don't have the problem (and I am assuming that many of them are running Time Machine using a networked storage device). Another possibility to explore, however, is that it could be related to using Time Machine to back up documents that were migrated to iCloud when configuring Sierra. For my situation, both upgrades to Sierra were accompanied by migrating the Documents folder to iCloud, so either Sierra itself or the Sierra implementation of Documents-in-iCloud could be the trigger.

This just happened to me last night after running Time Machine without issues for a very long time (years?). I have my backups going to a relatively new (since January) 4TB seagate backup drive that is connected via USB to my synology chassis. This has been working fine up until now. I am loathe to lose all my incremental backups even though it's only been a month. And from some of the comments, once started, this appears to be an on-going issue.

I came across this bit of information:http://jd-powered.net/notes/fixing-your-time-machine-backup but a not confident to try it. Has anyone else tried it or something like it? I am not very technical and am not confident that I could execute it successfully. And it's a bit old so not sure if would still work quite as stated.

Thanks

You can usually make your backups look as though nothing has happened, by following a procedure such as that one. Whether the data itself is actually corrupted or not is another matter. Flagging it as not corrupt does not fix any corruption that may have occurred.

I've been trying to track down this same issue. I'll admit I haven't read through this entire thread, but from what I've seen it appears to be a bug with Sierra for Macs that are backing up in certain situations (I've only seen it so far for Macs that are backing up to network drives via Ethernet). I have filed a bug report with Apple, so they're aware of the issue.

It does it to me using Mavericks (Yosemite gave me WiFi and BT issues that Apple was, ummmm, disinterested in fixing, so I went back to Mavericks, which had zero issues with those cutting edge technologies). The Mac in question was never upgraded to Yosemite.

I only have an Apple Time Capsule hardwired to the Mac. Hardly seems like a config they wouldn't have envisioned.

Apple is very aware of this problem.

Apple is very aware of this problem.

And has been for more than 6 years......so you will not likely see a solution from Apple in the near future. See the link below for more history and information on this issue.

http://pondini.org/TM/C13.html