Editable Plugin (SimpleMDE)

I'm having an issue with SimpleMDE editable plugin. It won't save when i click the tick button just displays a cross. I have created a modular page as seen in the screenshot below. Any idea what the issue is?
Content Page
Example - http://recordit.co/FE7datDeJi

You should raise an issue on the GitHub repo for the "Editable" plugin.

Yes, please raise a new issue here. Please add some extra info, such as the full page including header/frontmatter you are trying to edit, the route or path of that page. It helps finding the cause.
BTW your screencast shows the ContentTools editor, not the SimpleMDE editor.

I've just installed editable, it won't save either but I don't get a cross, if i inspect the page, i get a 500 error