We just got a new Nikon D7100 at work and are having an odd problem. Occasionally the shutter will not release when we try to take a picture. It appears to do this when there's not enough contrastn but through the viewvinder everything appears to be in focus. We're in program mode and unfortunately can't go to manual mode due to staff being unfamiliar with operation in that mode. We're using a Nikon 16-85 in autofocus mode with VR on.
I know this is something simple, but I'm not even sure where to start looking in the manual. How can we set up the camera to shoot when we push the release, regardless of focus/color/contrast, without going to full manual mode?