Sabine,
If you just added Facebook to the site, that's normal. Facebook takes a few days to 'see' your pages and check them for spam or 'bad' content. As long as your pages are reachable without being logged in (for now), eventually, Facebook will begin trusting all of your content.. even if it's for registered users only. For me, I'm not seeing that error, so it's probably already being approved by FB.
If by Friday or so you're still seeing the error, definitely let us know.
Thanks,
Alex
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