Could be the hidden option got enabled on them ( this would keep them from rendering ). But I don't think that's the problem. When thing like materials show up black in the labs, it's not a good sign. I only had it happen once with B4 and I never recovered the file. Something I do when working with scenes with complex objects. After I have an object created and positioned, I save it in the create library. That way if anything happens not all is lost. When I finish the project ( and have a file that open & close properly ), I delete the objects out of the library.

Stephen Ray