I Clicked on 3 of your buttons and I do not get a 404 page, It leads me to the top of your page as they are linked to #
I am not sure if you can open E&P in a popup, but you could try it.
Can you clarify what the process you took in details?
Have you considered trying X Lightbox?
You would add a light box selector to a raw code element and would add to the href of the button the content you want to open in the lightbox (the page with E&P) and also add to the button the class you chose as a lightbox selector.
Give it a go and let us know how it goes.