OK wow I see what you mean, it breaks badly just after pressing 'continuar' just after 3.1...

My best guess is that it some code in one of the HP5 exercises you're including on the page... very difficult to debug as they include a lot of code. I would start with removing them all (replace them with a plain HTML page as a 'placeholder') then add them back in one-by-one so you can find out which one breaks it.