Double-clicking on Set Doesn't add New Camera

If you are trying to add a new floating camera on set by double-clicking, but it is instead opening an object in the Green Room or giving you a message about a locked object, then the problem is either that

1. You are not in the blueprint View
   1. In this case you should switch to the blueprint view by double-clicking the blueprint view monitor always found in the top left hand corner of the main interface
2. You are not double-clicking on a completely clear area of the set but are instead clicking on some object.  In many cases this may be a floor object but regardless, you have to double-click on a completely clear area of the set to add a new camera.
   1. In this case, you should find an area on the set without ANYTHING on it, double-click to add your camera and then move it into position

Alternatively, if you have the Pro or Stereo Editions, you could instead drag in a physical camera from the Object Library.  To do so, go to the Props tab, choose Camera Equipment then Cameras and then drag in the desired one.