The sphere map node is a vestigial leftover from the days when Firefly needed cheats.

If you want a mirror ball, and you're using P12 and rendering in Superfly, I'd use the PhysicalSurface root.

But, the PoserSurface root will do. Try killing the Diffuse and Specular (set value to zero, set color to black). See what happens. Do you have the mirror ball in an environment, such as the construct? That enclosed environment will give the camera something to see in reflection. If I remember correctly, your Lincoln memorial image map would only show where there is no environment to be reflected.

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5