It is very easy. It's probably because of the SEF on your website. If you deactivate it, it will probably work.
So the solution is to edit the file terms of the view checkout via the menu Display->Views and change the line:
$text = '<a href="'.JRoute::_('index.php?option=com_content&view=article&id='.$terms_article.'&tmpl=component').'" class="modal" rel="{handler: \'iframe\', size: {x: 450, y: 480}}" target="_blank">'.$text.'</a>';
to include an Itemid of one of your article menu there. So for example, if you had a menu 48 with an article, you would have:
$text = '<a href="'.JRoute::_('index.php?option=com_content&view=article&id='.$terms_article.'&Itemid=48&tmpl=component').'" class="modal" rel="{handler: \'iframe\', size: {x: 450, y: 480}}" target="_blank">'.$text.'</a>';