Mailchimp subscribtion form problem


I'm using Popup pro plugin to show Mailchimp subscription form that I got from Mailchimp. The problem is, when the user click on "subscribe" button, the form will be submitted but I cannot get the AJAX callback to show a message to the user saying that "Your are successfully subscribed to the mailing list".

I believe that I have the same problem described in the following link:

Is there any solution for this?