Facebook Mail Delivery Failure?

[PEYMAN]

I sent someone a message in Facebook and I received this message few seconds later back:

"This message was created automatically by Facebook.
Based on the privacy settings of the person you're trying to contact, this message could not be delivered. Try sending them a Friend Request, wait until they accept it, and then try sending your message again."

The person hasn't blocked me (because I can send a message to the person)!
So, how would I receive such a reply from facebook?!
(I had blocked the person for some time though, now it's unblocked!)

[Lenny]

Because the user has set it to receive messages only from friends... therefore you must add the user in order to message them

[SouRabh Devani]

I don't agree with Lanny 'cause Facebook provides a feature of keeping strangers' messages out of inbox but not from "Other" folder. I've just checked it in my Privacy settings, in the "Who can contact me", it asks "Whose messages do I want filtered in my INBOX". There's no option of barring public from sending messages to you. Facebook is being unfair to you, dude; report this problem to Facebook. If they don't fix this, then spread this news through social media & social network that Facebook is unfair