Invite via email not working - Authentication progress bar stuck on 9%

The invite module doesn't depend on the Authentication or User plugins, so those shouldn't be a cause of any issues you're having. Unfortunately, however, I don't know the real issue is off-hand.

Are you able to send invites to Facebook friends as expected, and it's just email contacts that causes it to hang?

If you can post a link to your site, we can investigate further. Facebook's changed how the invites work a bit over the last month, and we're bug-hunting a few spotty issues that some users are encountering. Sorry for the inconvenience.

There's a couple of questions here. Usually, when someone posts that the email isn't coming, it's because they don't understand how the Invites work.

Facebook Invites are sent to the user's profile page. They show up in the right hand side under "Notifications", or something like that. If you're not selecting users from the list and you're using Step 2 which lets you type a user's email address in, if that email address is used for a Facebook account, it will still go to that user's profile page and not an email. Only if you type in an email address AND that user does not have a Facebook account will a real email be sent.

Personally, we don't like how the notifications appear on a user's profile page. They don't stand out enough. In the past, this has been more prominent, and we hope Facebook will make these notifications more bold again in the future.

Hope this helps clarify the notifications for invitations. Let me know if you're not actually seeing the notifications on your profile or if you are sending them to an email account of a user that doesn't have a Facebook account and they aren't going through.