When you program the chip. Nordic tools will check the CRC before and after writing the hex file to it. If the CRC is not the same then the tools will report that the flash operation has failed.
So, instead of calculating it from the flash, you can calculate it from the hex file you used to program the flash.
you use hex2bin.exe and crc.exe to calculate this and follow the procedure on page 2 in the below attached document.
