I have previously updated (5 month ago) the firmware to a "AT&T IoT Starter Kit (LTE-M)" without problem.
Now to an ":Add On Kit" I'm trying to change the firmware to the LTE-M.
Since I have the WNCCM and the drivers and the firmware for LTE-M (from the previous upgrade) i started the firmware change and I got the error below were to files are missing.
I uninstalled everything and reinstalled a newer version for the WNCCM and the same drivers and firmware. The problem remains the same.
Error Message from WNCCM::
Please check firmware image if exist adb.exe and fastboot.exe
The execution result: FAIL
Thanks in advance for your help