My mum has just got a Samsung Galaxy S4 and whenever she tries to make a call she is asked to double tap a lock icon after she has pressed the green call button and the call won't go through until she double taps. We can't work out why she can't just select the contact and press the green button! I'm an iPhone fan so not used to this phone. I've looked in settings to see if there is anything to disable but no joy. Can anyone please help?