Need help to burn bootloader on a Mega 2650

Hi! Me and my kids love our Makeblock mBot(mCore Atmega328) we are programming it for 3 years now.
Two weeks ago we bought a Makeblock Ranger(Auriga Mega 2650) and at first, it was working well.
Now when we try to upload our programme into the board it hangs randomly and if it goes up to 100% it fail mentioning that verification fails. We want to burn the bootloader on the Mega2650 using our Atmega328. I connected pins to pins for 5V, GND, MISO, MOSI, SCK and RST. Connected the Atmega to the USB port correctly connected to the port, loaded the sketch ArduinoISP, selected programmer Arduino as ISP and tried to burn the bootloader. This is what I have:

avrdude: Yikes! Invalid device signature.
Double check connections and try again, or use -F to override
this check.

Error while burning bootloader.

Any clue what is the problem? Kids are so sad that the new ranger is already dead...

Pictures of both boards.

Thanks.