OK – for the error where Facebook refuses to provide the event data, there’s not too much we can do to solve that on our end (it’s as simple as, we’re making the request via your account and they are saying “no”).
What we are going to try and do is capture additional data about the nature of the error, so that the reason for the refusal is less opaque. With that in mind, please do let me know if you hit additional errors of the same nature (ie, where you see the message about the even perhaps not existing, being private or Facebook refusing to serve it for content-based reasons).