Hmmm, that looks familiar. I got that error when I changed the fonts an Amibench tried to reset the screen (and couldn't due to open applications).
Last time I cancelled the process and quit Amibench before I got that error. It seemed to work at first. A restart of Amibench went fine and I finally had bigger font sizes. But after a new restart of Amibench I just got that grey screen error which I can't get rid of anymore.

Maybe something else crashed and I did not realise it?
Anyway, problem remains...