No Shading Group Associated Errors

Hey folks,

I have four similar scenes to render for a student film in maya software mode - all of them come from the same original file. The first three rendered beautifully, but I'm having a problem rendering the final scene. When I attempt to render it, all that shows up are the self-illuminated objects. Everything else in the shot is black. In reviewing the log, I've found multiple errors similar to this:

- building0022|window009|windowHeader001|polySurfaceShape3 has no shading group associated with it. This means that it will not be rendered. Please assign it to a shading group.

I've checked, and there are shaders assigned to all the objects. I've created new shaders and assigned them to objects with no change in their renderability.

I'm stumped at this point. Any suggestions?

Thanks in advance!