NRF9160 DK. "Failed to protect B0 flash, cancel startup" when building and running bootloader sample

[antas]

I understand correctly that in order to use my private key for my applications, I must first sign an immutable bootloader with this key and upload it to the device?

I used this tutorial. I opened the  samples/bootloader/ project.I did not find Use Secure Bootloader in the project settings, so I added this parameter to prj.conf (CONFIG_SECURE_BOOT=y), then I set path to my private key. After that I built and run it, but got "

*** Booting Zephyr OS build v2.1.99-ncs1-1-g8a6e96296c17  ***

Failed to protect B0 flash, cancel startup.

"

I also erased the chip via Target > Connect J-Link and then Target > Erase All, but it didn't help

[Amanda Hsieh]

Hi, 

Please see shibshab's suggestion in this post. 

-Amanda H.