Can't backup with Time Machine in OS Sierra

Yes, Sierra is a problem.

Factory reset the TC and redo the setup. Follow the following.

For Sierra make sure you have no Anti-Virus software installed.. if you upgrade installed and used to have any of them remove it.. including security or firewall software and anything that even comes close to being adware.

Factory reset universal

Power off the TC.. ie pull the power cord or power off at the wall.. wait 10sec.. hold in the reset button.. be gentle.. power on again still holding in reset.. and keep holding it in for another 10sec. You may need some help as it is hard to both hold in reset and apply power. It will show success by rapidly blinking the front led. Release the reset.. and wait a couple of min for the TC to reset and come back with factory settings. If the front LED doesn’t blink rapidly you missed it and simply try again. The reset is fairly fragile in these.. press it so you feel it just click and no more.. I have seen people bend the lever or even break it. I use a toothpick as tool.

N.B. None of your files on the hard disk of the TC are deleted.. this simply clears out the router settings of the TC.

Setup the TC again.

Then redo the setup from the computer you want to use for TM using Airport Utility.

1. Use very short names.. NOT APPLE RECOMMENDED names. No spaces and pure alphanumerics.

eg TCgen5 for basestation and TCwifi wireless name.

If the wireless is still a problem set wireless names like TC24ghz and set the 5ghz to different name.. eg.TC5ghz

2. Use all passwords that also comply with 1. but can be a bit longer. ie 8-20 characters mixed case and numbers.. no non-alphanumerics.

**3. If the TC is main router you can skip this point. This is only an issue when the TC is bridged.

Ensure the TC always takes the same IP address.. you will need to do this on the main router using dhcp reservation.. or a bit more complex setup using static IP in the TC.

Ignore this point if you don't understand it .. post back if you have drop out issues.

4. Make sure IPv6 is set correctly in the computer. ie link-local only for ethernet and/or wireless depending on which you use. Auto is not good enough.

Make sure your computer is directly connected to the TC.. not via another router.

The problem is, even doing the above might make the backup work for a few weeks and then Sierra will wipe it out due to corruption and start over. So we strongly recommend for the moment.

1. Use a USB self powered drive plugged directly to the computer and set that as your Time Machine target. It is faster and much more reliable.

2. Use Carbon Copy Cloner or other suitable third party backup software eg Chronosync.. which can be used to the TC with a sparsebundle the same as TM uses. CCC is reasonably price and a lot less troublesome.. for the moment.