DIYBMS - Upload cell module - Error 1 target doesn´t answer

Hi everyone,

I try to program 4 cell modules, V4.21. I always get the error message:

avrdude: error: program enable: target doesn’t answer. 1
avrdude: initialization failed, rc=-1
Double check connections and try again, or use -F to override
this check.

The green LED on the board starts to flash for about 3 seconds and than appears the error message.
Since I have little idea about programming, I would be happy to receive support

Thx, Rudi