I was running into a problem on a multi-page form on Chrome not submitting. (It works on other browsers - IE, Firefox, Safari). I got the error "An invalid form control with name='input_35' is not focusable". After some research on-line, it appears this happens when an HTML5 form input cannot be validated properly but isn't necessarily visible on the page. In my case, it turned out to be a numerical input that was set to a decimal range of values (min:0.0 to max:4.5).
In the HTML5 specification, you should apparently set your "step"='all' in order to support decimal point increments; however, it is not clear how to do this within Gravity Forms as there are only fields for min/max, not step. I have disabled HTML5 form outputs and solved my immediate issue; however, I would appreciate being able to use HTML5 form controls and still submit my form.