MacBook Pro with arduino R3 refuses to react

Hi Gys,
I am completely new to this so excuse if I sound a bit stupid.
I bought a Rluiiguu Arduino R3 and it works well with my MacMini OS mojave.
But on the go or on occasion I need to use a laptop and my (Very old) MacBook Pro refuses to cooperate.
It runs on OS ElCapitan
and I got this error message:

Arduino: 1.8.9 (Mac OS X), Board: "Arduino/Genuino Uno"

Sketch uses 942 bytes (2%) of program storage space. Maximum is 32256 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 2039 bytes for local variables. Maximum is 2048 bytes.
/Applications/Arduino.app/Contents/Java/hardware/tools/avr/bin/avrdude -C/Applications/Arduino.app/Contents/Java/hardware/tools/avr/etc/avrdude.conf -v -patmega328p -carduino -P/dev/cu.usbmodem1A21 -b115200 -D -Uflash:w:/var/folders/cp/22db3sn16kx5pcfwgt9shwlw0000gn/T/arduino_build_523450/Blinking_LED_Code.ino.hex:i

avrdude: Version 6.3-20171130
Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
Copyright (c) 2007-2014 Joerg Wunsch

System wide configuration file is "/Applications/Arduino.app/Contents/Java/hardware/tools/avr/etc/avrdude.conf"
User configuration file is "/Users/poohsmcbp/.avrduderc"
User configuration file does not exist or is not a regular file, skipping

Using Port : /dev/cu.usbmodem1A21
Using Programmer : arduino
Overriding Baud Rate : 115200
AVR Part : ATmega328P
Chip Erase delay : 9000 us
PAGEL : PD7
BS2 : PC2
RESET disposition : dedicated
RETRY pulse : SCK
serial program mode : yes
parallel program mode : yes
Timeout : 200
StabDelay : 100
CmdexeDelay : 25
SyncLoops : 32
ByteDelay : 0
PollIndex : 3
PollValue : 0x53
Memory Detail :

Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack


eeprom 65 20 4 0 no 1024 4 0 3600 3600 0xff 0xff
flash 65 6 128 0 yes 32768 128 256 4500 4500 0xff 0xff
lfuse 0 0 0 0 no 1 0 0 4500 4500 0x00 0x00
hfuse 0 0 0 0 no 1 0 0 4500 4500 0x00 0x00
efuse 0 0 0 0 no 1 0 0 4500 4500 0x00 0x00
lock 0 0 0 0 no 1 0 0 4500 4500 0x00 0x00
calibration 0 0 0 0 no 1 0 0 0 0 0x00 0x00
signature 0 0 0 0 no 3 0 0 0 0 0x00 0x00

Programmer Type : Arduino
Description : Arduino
avrdude: stk500_recv(): programmer is not responding
Hardware Version: 3
Firmware Version: 4.4
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding
Vtarget : 322122197.6 V
Varef : 21918.2 V
Oscillator : Off
SCK period : 562222.3 us

avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding
avrdude: initialization failed, rc=-1
Double check connections and try again, or use -F to override
this check.

avrdude: stk500_recv(): programmer is not responding

avrdude done. Thank you.

Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

If someone can help me I would be grateful
Paeppchen AKA Rolf

Make sure you have selected the port of your Arduino board from the Tools > Port menu.

Sometimes the port will be labeled with the board name in the menu. Other times it will not. If you don’t know which port is your Arduino, you can find it like this:

  • Unplug your Arduino board from the computer.
  • Tools > Port
  • Note the ports, if any, listed in the menu.
  • Close the Tools menu
  • Plug your Arduino board into the computer.
  • Tools > Port - The new port listed in the menu is your Arduino board.