That article does look to be a registered article, but no, that's usually not the cause. Basically, your correct that Facebook can't see the page because it's redirecting. However, these issues usually go away after a few days if you've recently added comments to your site, and some are hidden from Facebook's prying eyes. We honestly don't know what gets 'fixed', but in general, we know that Facebook wants to know what's on pages to verify that your site isn't malicious or spammy.
We think this is how it works, but can't guarantee:
* If you have pages that are public, they can infer that the non-public ones are ok.
* Additionally, when a registered user views those pages, since the Facebook library loads, they can gather some information from the page itself (looking at the Open Graph tags if they exist or the meta tags).
* Once Facebook's seen enough pages from your site through either of the methods above, it stops with the those messages.
Again, this is our guess, but this question comes up here and there with new applications and/or heavily 'private' site (mostly registered only). It's almost always resolved itself, but you will need to have some patience. If, in a few days, you're still seeing these messages, definitely post back here and we can investigate further.
Thanks,
Alex
Warning: URL is unreachable
