Ctrl-Ap indicates that the device is secured

[NRM]

Hello,
I can run "nRF5_SDK_15.2.0_9412b96" examples with the nrf52840 eval kit pca10056/s140 without any problem, but I can't run the same examples with custom board.
all examples that need to be uploaded soft device before the main program in Keil build perfectly, but after downloading during the programming process “ctrl -ap indicates that the device is secured” appear.
Other examples do not have this problem.

Best regards,
NRM

[Kenneth]

Hello,

I suspect the nRF52840 board are now mounted with the latest revision 3 of the nRF52840, which include some changes that require the latest nRF5 SDK 17.1.0 or that you need to update the MDK files on older nRF5 SDK
Description of change: https://infocenter.nordicsemi.com/pdf/in_141_v1.1.pdf
Compatibility: https://infocenter.nordicsemi.com/topic/comp_matrix_nrf52840/COMP/nrf52840/nRF52840_ic_rev_sdk_sd_comp_matrix.html 

A description on how to update to new MDK (device family pack) in Keil for older nRF5 SDK is described here:

 RE: MDK uVision SDK 16.0 keil Family Pack Installation  

Best regards,
Kenneth

[NRM]

I try nrf5 SDK 17.1.0 example but it doesn’t work and the problem still remains, also MDK updated for latest version.
how can I disable the access port protection in command line for APPROTECT.DISABLE?
Even though I follow all the instructions in this guide, the same error persists.
I will very grateful if you tell me what can I do step by step, that this problem solve.