Verification and message fails

I use the plugin to add a “Request info” button on each page of the catalog to open a request form on the site of my client under development.
Use WP 3.5.2, base theme with w7 (tested on chrome, firefox and IE) and gravity forms 1.7.6. No others plugins are activated except Maintenance Mode.

After click the “send button” the form close and do not show the answer in both case of an missing or error formatting the mandatory field or succes sending.

If I reclick the “Request info” button on the same page the message (error or succes) is shown until I change page or post also if I close the message. In case of error the message is shown at full page. See here
https://www.romantiquariato.it/img/fullpagemoduleerror.JPG

If I try to refresh the page ex: F5 appear this system message:
The page that you are trying to access uses information that you entered. Returning to that page might cause any action that you took to be repeated.

NOTE
The form have a hidden field {embed_post:post_title} that send the page title via Email.
If all the mandatory filed are correct the mail in correctly sended.

https://www.ads-software.com/extend/plugins/gravity-forms-popup-widget/