I've done a lot of reading about this and most people point to not having a verified email address specified as your primary contact in your Facebook profile, but I've checked that and removed/re-added my email addresses several times to make sure it's not that.
I also asked a few of my members to test the integration by trying to link their forum accounts with their Facebook profiles, but in every case they got the error about an email address not being returned.
Here are my Facebook App setup details:
... now interestingly, I have had no difficulty disassociating my xenforo.com forum account with my facebook profile and then re-adding it again. So I'm pretty sure that there is nothing wrong with my Facebook account.
I read somewhere about using the Graph API Explorer to test whether the email address is returned correctly:
... which it is ...
... I'm at a loss as to what else to try to troubleshoot this issue.
I also tried setting up Facebook integration with one of my other XenForo forums and had the same problem - so I don't think it's specific to my XenForo installation.