Can't read GPIO pin 4

Hi, i can't read the value of of pin 4 with Matlab (and/or Simulink) every other pin is working. Has anybody an idea? thanks in advance!

mypi = 

raspi with properties:

         DeviceAddress: 192.168.178.25                
                  Port: 18730                         
             BoardName: Raspberry Pi 2 Model B        
         AvailableLEDs: {'led0'}                      
  AvailableDigitalPins: [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27]
  AvailableSPIChannels: {}                            
     AvailableI2CBuses: {'i2c-1'}                     
      AvailableWebcams: {}                            
           I2CBusSpeed: 0                             

Supported peripherals

>> readDigitalPin(mypi,4)
Reference to non-existent field 'gpio4'.

Error in raspi/readDigitalPin (line 565)
          if ~obj.DigitalPin.(pinName).Opened

>>