Using nrfjprog version 9.7.2 on Windows 7 Professional. Just discovered that when .hex file is read-only, nrfjprog fails.
>nrfjprog --verify --program app.hex
Parsing hex file.
ERROR: The file specified could not be open for read.
Removing the read-only property:
>nrfjprog --verify --program app.hex
Parsing hex file.
Reading flash area to program to guarantee it is erased.
Checking that the area to write is not protected.
Programing device.
Verifying programming.
Verified OK.