When I look at my Atom feed (http://www.technomad.be/blog/feed/atom/), I get the same error "ERROR: atom is not a valid feed template". All settings are put in correctly in admin - settings - writing).
When I try to validate the atom feed in W3C, I get "Server returned HTTP Error 500: Internal Server Error".
All other feeds (rss,rdf,...) work correctly en validate ok.
Since my blog is in dutch and use special characters, I implemented all changes suggested here (http://www.w3it.org/blog/wordpress-feed-error-output-solution-how-to/) with the same result: all feeds work, except the atom feed.
Any ideas what is going wrong?
For some reason when opening the atom feed url, the secure login for the wp-admin folder is required. But even with the right login the result is the same: all feeds work, except the atom feed.
:-(