Can't add RSS Feed

I have two subsites with posts I’d like to show on main site but even validated (with feedvalidator.org) RSS Feeds shows “RSS Error: WP HTTP Error: A valid URL was not provided”

These are the feeds

http://blog.epet1.edu.ar/feed/

http://docentes.epet1.edu.ar/construcciones/feed/

However, must say that validation was just passed after fixing errors

Any clue will be much appreciated.