error: Serial port '/dev/tty.usbserial-A4005g8U' already in use.

hello, i have a trubble then trying upload my script(first script example) to arduino (ATmega 328) on Mac

error: Serial port '/dev/tty.usbserial-A4005g8U' already in use. Try quiting any programs that may be using it. i don't run any program to use any port

May be anybody knows what's wrong?

Are you sure you don't have any other program using the serial port? Try to restart the computer and then ONLY open the Arduino IDE and try to upload then.

Jan