Arduino and Matlan2014b interface

I have a matlab 2014b on my mac and have installed arduino I/O package. I was trying to turn on/off a led through arduino but the matlab keep on showing an error.

delete(instrfind({'Port'},{'/dev/tty.wchusbserial1420'}))  
a= serial('/dev/tty.wchusbserial1420');
fopen(a);
configureDigitalPin (a,22, 'output');
writeDigitalPin(a, 22 , 1);
for i = 1:10
    writeDigitalPin(a, 22, 1);
    pause(0.5);
    writeDigitalPin(a, 22, 0);
    pause(0.5);
end
Warning: Unsuccessful read: A timeout occurred before the Terminator was reached.. 
  Error using arduino (line 104)
  Connection unsuccessful, please make sure that the board is powered on, running a sketch provided with the package, and connected to
  the indicated serial port. You might also try to unplug and re-plug the USB cable before attempting a reconnection.

How to resolve this problem.
Thank you.