I'm using MacOS X El Capitan, vers 10.11.6, and Arduino UNO, and when trying to connect the computer with Arduino I get the following message:
cant open device "/dev/cu.usbmodemFD131": no such file or directory
How can I solve this problem?

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.

Thank you for your help, I’ve solved my problem following your tips.
Using a board with USB mini type connector there is not any problem, port is FD131,
but using a USB B type I need to choose an other port an the system runs.

You're welcome. I'm glad to hear it's working now. Enjoy!

Happiness destroyed!
Changing port avoided the error message about usbmodemFD131, but a new problem appears whwn trying upload an sketch. i've looked for this error in the Forum and I've found that is a very commom failure.
I have four different origin boards, two of them work perfectly, but in the other two have the problems indicated before.
I'm a recent Arduino user, and I conclude that some origin of the boards may be not recommended and we need do an accurate board choose.

Different boards may enumerate to different port names. You need to make sure the Tools > Port menu selection is correct after connecting each board.

Finally I’ve solved the problem, the thing is that I’m a new Arduino user and I don’t kwon a lot of elementary items I should know.
The solution is a contribution of one of the board suppliers. Before today I thougt all boars have the same modem, but it isn’t, this supplier told me that I needed download an specific driver, I did and all it’s OK.
Thank you everybody.
I think that’s an interesting item for the new Arduino users