Hi! Make sure that you have selected the right serial port in the Arduino IDE (from the Tools menu). If the error still persists, try to move the IDE installation directory to a path that does not contain spaces -- it causes errors for the Windows version of the program, so I think it can do the same also on MacOS.
Hope this helps!
Thank you! the problem was that I renamed the file (Arduino Galileo) just to be sure of compatibility issues with the libraries I use with the "old" arduino IDE.. Changing the name solved the problem.