After trying almost all your list of tips, I couldnt open the file properly on the slave... and discovered the pb !
I knew this was a stupid noob problem ^^
As the slave is not connected to internet, I had to update Max version to 2020.3 manually, and forgot to install first 2020.1 and .2 ....
Everything rune fine now thanks for the assistance !!
Regards,
JG