I have installed a additional circuit board 3lines 8 extensions(number 3) on a existing ZEN Topaz that already works with 6 lines and 16 extns. The extensions are working fine but I cannot get the exchange lines to work. There was 2 exchange port left on the second card which I'm now using but we need one more to work on position 7. Is there a part in the program that I'm missing to activate the lines? or a physical switch?