To reproduce:
(with-temp-buffer
(auto-revert-mode)
(kill-buffer (current-buffer))
(auto-revert-buffers))
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.