Backup failed

Please check the integrity of your backups as follows:

Hold down the option key on your Mac while you click on the Time Machine "clock" icon at the top of the Mac's screen

Click on Verify Backups

The process will take anywhere from 10-60 minutes or more, depending on how much data is present on the Time Capsule drive

Post back on your results

Stock standard issue on Sierra and High Sierra unfortunately.

Happens on earlier versions as well without the frequency.

Reboot the whole network.. restart in correct order.

1. Modem.. wait 2min

2. Time Capsule (I am guessing).. wait 2min

3. Computers etc.

If that still doesn't work we need more details.

What OS are you on?

How does the TC (confirmation please) connect into the network and how does the iMac connect to it??

What make and model is the main modem?

Is it working in bridge or as main router?

Is the TC working in bridge or as main router?

Fill in the details and perhaps even a few screenshots will help loads to figure out how to help you.

I have exactly the same message with the same dates. Updating the firmware on the airport station was not possible as the firmware version was the same as in the reply by support. Hence still the same problem.

Give us screenshots of your setup from airport utility.

It also helps to know the full layout of the network. Main modem router? How the Time Capsule is connected and in what mode? As well as what OS on the computer and how it connects.. ie ethernet or wireless.

Without details we really cannot help.

Is your Mac running macOS Sierra or High Sierra? Are you running Time Machine (TM) backups to a Time Capsule (TC) or to a drive directly attached to your Mac?