Grant Extended Permissions not working

I have been having a lot of trouble getting Ultimate Facebook to grant extended permissions so that I can have it post when I add a new post/page/product.

I have been right through the forums and documentation several times, and tried lots of things (for about a week) and no luck.

I am not sure whether this message is going to post publicly on the forum, so I don't want to give too much detail, but I do have screen shots I can send if you need them. I have the FB app set up and have put the app id and secret key into the plugin settings page, and it accepts these and says it is successfully connected. But when I click the Grant Extended Permissions link, on either the plugin settings page or the Add Post page, I get this . Basically the window pops up and then goes away and nothing changes.

I have deleted and recreated the app several times, and also tried this on three different hosting platforms. The same thing happened when I tried it on a fresh WP install with no other plugins and the default theme.

In the Facebook side, Dashboard says "This app is public and available to all users". Settings has the domain name (both without the www) in App Domain and Site URL (under "Website" platform). Also has my email address in place. Status & Review has Yes to make it public, and, under Approved items, has Email, Public_Profile and User_Friends approved.App Details has these filled in: App Details, Short Description, Explanation For Permissions, Privacy Policy URL, Terms of Service URL, User Support email. Also has Yes on Website under App Center Listed Platforms, and app icons are uploaded.

I have tried lots of combinations of all of the above, following suggestions in the forums, with no luck. Help please? What have I missed?