This is a common error if you haven't got my "LightWorks in Archicad" book.
When you make a new material and seek to employ it in the LightWorks Rendering Engine you need to do some extra work. If you made the material in the Material dialog, its values must be transferred to the LightWorks Engine by switching to the LightWorks Engine and clicking "Match Internal Engine"
This process moves the image and its settings to the LightWorks Engine that can then be seen in Lightworks renderings.
Dwight Atkinson