Happened to me just yesterday - was working on a box modelled object, UV unwrapped, exported layout, painted in Krita and imported back into Blender.
Rendered it in Cycles, only to find that my model disappeared.
Removing the material did nothing, and all the options that could've avoided it from showing up were disabled.
Only thing that fixed it was to save entire scene to new .blend file and open, unselecting "Import UI" or whatever it's called and retexture everything.
I wasn't going to use Cycles, as most people here shit on it more than on Blender itself, but RenderMan and POV-ray decided to just not work.