Since several days, I can no longer add application tabs to pages. The options for viewing the application page, and then click the "Add to my page" button, have disappeared. Please, help!
Thank!
This has changed since a few weeks, now you need to call this URL:
https://www.facebook.com/dialog/pagetab?app_id=YOUR_APP_ID&next=YOUR_URL
Replace YOUR_APP_ID with the application identifier and YOUR_URL with the URL that the application is running in - keep in mind that this must be a valid and existing URL!