Andreas Röhler <andreas.roehler@easy-emacs.de> writes:

You asked for a diary file. Don't have that. But have a file SOME.org
in that directory, where diary-fancy-display is looking into. Which
shouldn't matter WRT bug, just because you asked.

~/.emacs.d/diary should be a file, not a directory.  Having that be a
directory is not supported.

Let assume the user had such a file. Now it got deleted. Which results in that spurious error.

Instead of that opaque error, a warning could be sent - likewise, preventing it internally seems an option.