Unable to flash conbee 2 on windows. Got correct firmware

Hi,

I got a Windows 10, fully patched.
I downloaded latest GCFFlasher and latest firmware for my Conbee II.

When executing following command I get following error :

C:\Users\johan\AppData\Local\dresden-elektronik\deCONZ\firmware>GCFFlasher -d COM4 -c -t 100 -f deCONZ_ConBeeII_0x26780700.bin.GCF
read file success: deCONZ_ConBeeII_0x26780700.bin.GCF (163244 bytes)
flash firmware
connect \.\COM4, baudrate 115200
command reset timeout
connect \.\COM4, baudrate 115200
query bootloader id V1
query bootloader id V1
query bootloader failed
retry: 91 seconds left
read file success: deCONZ_ConBeeII_0x26780700.bin.GCF (163244 bytes)
flash firmware
command reset timeout
connect \.\COM4, baudrate 115200
query bootloader id V1
query bootloader id V1
query bootloader failed
retry: 87 seconds left

Your advice is much needed.

Br.