GMail Contextual Gadget not working

I'm trying to deploy a contextual gadget in my domain. I have followed the development guides but the gadget does not show up. I think that the problem is about "Data access": event if the installation seems to go smooth, in the Google Apps console the data access section of the gadget shows a red X. If I try to grant access by pressing the specific link, nothing happens and a blank page appears. I am using a superadmin user.

I have tried in two different domains with no success.

Here the is manifest:

<?xml version="1.0" encoding="UTF-8" ?>
<ApplicationManifest xmlns="http://schemas.google.com/ApplicationManifest/2009">

  <Name>My Gadget</Name>

  <Description>
    Sample Gadget  
  </Description>

  <Extension id="SinesyExtractor" type="contextExtractor">
    <Name>My Stuff</Name>
    <Url>google.com:EmailBodyExtractor</Url>
    <Triggers ref="MyGadget"/>
    <Scope ref="emailBody"/>
    <Container name="mail"/>
  </Extension>

  <Extension id="MyGadget" type="gadget">
    <Name>Gmail contextual gadget</Name>
    <Url>http://download.XXXXXX.it:8080/download/gmail/XXXXXX.xml</Url>
    <Container name="mail"/>
  </Extension>

  <Scope id="emailBody">
    <Url>tag:google.com,2010:auth/contextual/extractor/BODY</Url>
    <Reason>
      This application searches the message body of each email for text related to Add-in Express products.
    </Reason>
  </Scope>

</ApplicationManifest>

Have you a suggestion or a link to a guide I can follow?

Thanks, Lorenzo

The root of the issue here lies in the fact that the Developer Guidelines for the contextual gadget are outdated. Google deprecated that way of authentication in the admin panel in November 2013 but did not update the contextual gadget page.

Creating a new project and following these steps fixed the "Grant Data" problem that you are experiencing.