You could try right-clicking on a chair and selecting LightUp-Vertex Lit from the context menu. If it works, do that to each chair.
Is the chair from the 3DWarehouse? If so, which one? The chairs on 3D Warehouse have no quality control and, though they may look ok in SketchUp, may be badly formed with reversed/overlapping/intersecting faces. If that is the case, it is necessary to either correct the errors (possibly a difficult and tedious task) or try a new chair.
LightUp is a remarkable renderer, but all renderers have trouble with malformed geometry.