Uwe Brauer <oub@mat.ucm.es> writes:

> I using a pretty old package called org-fstree
> <http://www.burtzlaff.de/org-fstree/org-fstree.el>
>
> All it requires, after loading it of course, is  to have in an org file the lines
> --8<---------------cut here---------------start------------->8---
>
> #+begin_fstree: /home/oub/ALLES/HGs/HG-CVS-Formular :non-recursive t
>
> #+end_fstree:
> --8<---------------cut here---------------end--------------->8---
> ...
>
> However not any longer when I now hit C-c C-c org tells me:
> can't do anything useful here.
>
>
> I updated org-mode recently could that be the reason? I have changed my emacs version lately.

Is you see "can't do anything useful here", it most likely means that
you did not load the package.

http://www.burtzlaff.de/org-fstree/org-fstree.el has (add-hook
'org-ctrl-c-ctrl-c-hook 'org-fstree-apply-maybe)
which should make things work, unless you somehow do not load the
package.

When I tried on my side, things work, except that I had to change
"reduce" calls to "cl-reduce" - "reduce" name alias has been deprecated
and removed Emacs 27.

I am attaching the modified working version of the package.