Serial communications crashes when accessing an array

I'd been making a project involving serial communication between arduino and matlab 2016a.

So far, the communication was successful, but when i try to use the data received from arduino, the serial communication disconnected.

The arduino code is:

    Serial.println(String(flexread1)+" "+String(flexread2)+" "+String(flexread3)+" "+String(flexread4));

The matlab code is:

 disp('Initializing Serial...')
 mcu=serial('COM6', 'BaudRate', 3000);
 fopen(mcu);
 try
    while(true)
        chk=str2num(fscanf(mcu));
        getnum=chk(1);
    end
 catch 
    fclose(mcu);
    disp('Serial closed..')
 end

The command window displays

 Initializing Serial...
 Serial closed..

If I were to use getnum=chk; the array sent from arduino was able to be saved successfully into getnum, but the moment i used getnum=chk(1); the comunication got disconnected. Playing around with baudrate doesnt help.