VideoCapture always return null image using industrial camera

I always used VideoCapture to take frames from webcams but since I've used an industrial camera (the david laser scanner one, 3_M), VideoCapture objects always returns a null image. I've already known I have to change the ID numbers in the VideoCapture constructor but the problem still remains.

VideoCapture cap(0);
cap>>image; // this function return a null image

If I use grap and retrieve

bool t = cap.grab(); //returns true
t = cap.retrieve(image); //returns false

Does anyone know the reason why this problem happens?

I tried this new camera using both the david scanner sw and skype and it works perfectly so it should not be neither an HW problem nor an OS driver one.

Thank you