There seems to be something wrong with the Related Articles section. When I do a View Source of that page, it ends right after the first related article link (Los tiempos del Ródano), so the code for the sidebar never gets generated. I don’t know if there’s a plug-in that generates the Related Articles section, but you can try disabling it to see if that fixes the problem. If so, then you’ll have to try and figure out what related articles the plugin is trying to put there.
Rewrite the post and don’t copy any content from a Rich Text Editor. To test that one post just type ‘test’ in the visual tab and update…