Macbook 2016 stuck in an update loop

In trying to set up and log into my new Macbook Pro 15" with TouchBar, I got only as far as entering my network information when I received the error message:

A critical software update is required for your Mac, but an error was encountered while installing this update. Your mac can't be used until this update is installed.

On the advice of others posting here, I did a re-install of the OS from Command-R. This did not help me. I tried several times.

Then (also from within Command-R) I erased and re-formatted the hard drive, re-installed the OS, and for the first time was able to get as far as inputting my time zone and setting up a user account.

The first thing I did once I finally gained access to my new computer was to visit the App Store and download updates. One of the App Store system updates needed a re-start.

When the computer re-started, it made it to the log-in screen. However, after I entered my password, the screen froze, with a spinning beach ball. I was not able to login again to the account.

I did a hard re-start. When the system started again, I was prompted for my WIFI network, and then received the same error message:

A critical software update is required for your Mac, but an error was encountered while installing this update. Your mac can't be used until this update is installed.

Help??!