The ZMD-DR-SFN6 is unable to view all 16 cameras at once. Instead, you have to cycle through the cameras, 4 at a time.
To do this, keep clicking the button that says '4' in the upper-right corner of the interface.
Cameras 1-4
Cameras 5-8
Cameras 9-12
Cameras 13-16
You can just keep hitting the '4' button and rotate through all 16 cameras that you have hooked up.
Tags: camera, can't view, shortage