How to stop loading screen after form is submitted

Hi, I have created a popup which contains a form that submits via ajax. When I send the form, the popup shows a loading screen. But after the form is sent, the loading screen never stops. The popup keeps "loading" forever.

I think it has to do with this setting: but I already tried all the options with no luck.
https://docs.google.com/file/d/0B6nmyp5p7PnYOGhkQkpjQ1EzZ2M/edit?usp=drivesdk