We confirm our view that zero or small overlap between individual subsystems of a larger system due to spatial separation causes a failure of present-day time-dependent density-functional theory methods for certain excitation energies. This view, very generally, covers typical charge-transfer excitations between a donor and an acceptor as first analysed by Dreuw and Head-Gordon, excitations in symmetric supersystems with spatially well-separated components without donor-acceptor character, as well as cases lying inbetween. (c) 2006 Elsevier B.V. All rights reserved.