Hi, I have this same issue right now and enter here to search for a possible solutions. ...was about to add a new ticket but I guess I should use this same one. I have noticed that when pasting the form's html code to my squeeze page, WP's html editor distorses the design of the form (it separates all the elements and the form from the page's content). When saving and testing the form like 'as is' the form work ok but the squeeze page design is all 'crippled'. When at the visual HTML editor I remove, or try to because it just doesn't let to remove all the space that separates all the form fields and the space form it self from page's content... is when the form stops working and replies with this error. If you look at the html code it just looks ok. I even tried to add it inside tables, outside, etc.
Viewing the form from the button @ the form's configuration, the form design present just greate (very compact and in place) and works just fine. Yesterday @ github I askd if there's a shortcode to add the form to a squeeze page mainly because of the design issue... but all day today I've been struggling with the issue that besides the design and/or display the form stop's working also if trying it to edited in the visual html editor.