I have several Arduino Dock 2 boards and for some of them when trying to program the
Arduino AVR chip on the Dock using the Omega (2+), they give an error message "Communication Failure". Other Dock 2 boards of the same typ work fine. For the ones that are not working I am trying to program them using a spare Arduino Uno as a programmer. I successfully program one Uno from another Uno using the SPI signals as instructed here:
https://www.instructables.com/Programming-Arduino-With-Another-Arduino/

That works fine, so I connected the non-working Dock 2 using the same wiring scheme (11, 12, 13 SPI lines, 10 from programmer to reset on the Dock 2 and 5V pwr and gnd). There is no Onion Omega plugged into the Dock2. I have ArduinoISP loaded into the Uno and I try to upload Blink.ino by clicking 'Upload using Programmer". It seems to write to the Dock2 and tries repeatedly to read and verify the code, then issues the following error message:

avrdude: Device signature = 0xffffff (probably .avr8x_mega)
avrdude: Yikes! Invalid device signature.
Double check connections and try again, or use -F to override
this check.

It's the same whether I set "Arduino Uno" or "Onion Arduino Dock" as the target board.

If I run avrdude from the command line with the -F switch as

avrdude -F -C../etc/avrdude.conf -v -patmega328p -cstk500v1 -PCOM8 -b19200 -Uflash:w:C:\Users\GOLDMA~1\AppData\Local\Temp\arduino_build_728892/Blink.ino.hex:i

it gets further, but then gives this new error:

avrdude: verifying ...
avrdude: verification error, first mismatch at byte 0x0000
0xff != 0x0c
avrdude: verification error; content mismatch

avrdude: safemode: hfuse reads as FF
avrdude: safemode: efuse reads as FF
avrdude: safemode: Fuses OK (E:FF, H:FF, L:FF)

A similar error comes back if I try to load a bootloader into the Docks with the Arduino "Burn Bootloader" command.

Would someone provide detailed instructions for programming the AVR chip on an Arduino Dock 2 via the SPI interface or from a spare Arduino?

Thanks.

I had problems with configuring UNO as ISP. It was long time back, so I don't remember the exact error codes, but I remember that the UNO programmed
using IDE 1.6.x to act as an ISP failed to program the "3rd" UNO.

All versions of IDEs are not good for the job.

Finally, I was able to program the 3rd UNO using the 2nd UNO (ISP) which is
programmed into an ISP using the 1st UNO with IDE 1.0.1.

https://www.instructables.com/Burning-the-Bootloader-on-ATMega328-using-Arduino-/

I still have that ISP UNO, and it can work as ISP with other versions of IDE such
as 1.8.x

Thanks..