Serial port '/dev/tty.usbmodem1411' not found. on Mac OSX

I am using Arduino Uno board and I cannot find usb modem under tools > serial port.
I know there is no problem with my usb cable or my computer's usb port because I have another Ardiuno uno board which perfectly connects to the computer and uploads programs.
Why do I get this message and how can I prevent it?
Thank you... :slight_smile: