Ok,

I believe the problem is with named components.  In the old eieio, it
allowed nil names, but in the current implementation it requires a name for
named components.

A work-around in ergoemacs-mode shows the possible issue

https://github.com/ergoemacs/ergoemacs-mode/commit/71319c2cc1874248c885cd6b6e7f826fb24c49a7

Matt.

On Sun, Mar 29, 2015 at 7:47 PM, Stefan Monnier <monnier@iro.umontreal.ca>
wrote:

> > Since I'm here I would also like to add that eieio doesn't work the same
> in
> > emacs 25.
>
> There's been many changes to EIEIO's internals, indeed.  I've tried to
> preserve compatibility so far both for source files and for
> byte-compiled files (tho not for files byte-compiled with non-released
> Emacs versions).
> So if you experience incompatibilities because of the new code, please
> report them,
>
>
>         Stefan
>