Black HDRI Background ...
 

I’ve added a HDRI background through the IBL option in “Indirect Lighting” in Render Settings. Everything is fine to this point. I’ve set my camera’s background color to white and I get the expected resulting render. Now, however, when I try to swap out the HDRI image, using the “Image Name” box, I get a black background along with “Warning” prompt ... a grab of which I’ve attached. Even going back to the original HDRI file doesn’t correct the issue. What gives ???