The function is usually called from a timer, which means that if a killed buffer somehow ends in `auto-revert-buffer-list', Emacs becomes nearly unusable, because it spams with this error message non-stop.

I don't know how exactly a killed buffer can end there, but it has happened to me several times already, probably after extensive C-g use.

`auto-revert-buffers' must be fixed to never select killed buffers.