Scusate ho anche io lo stesso problema.
Gli open graph sembrano così ostici da usare nonostante la semplicità apparente.

Ho una semplice pagina php

codice:
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:fb="http://www.facebook.com/2008/fbml" xmlns:og="http://ogp.me/ns#"><head>
<title>Pippo e Pluto</title>
<!-- facebook -->
<meta property="og:locale" content="it_IT">
<meta property="og:type" content="website">
<meta property="og:title" content="Pippo e pluto">
<meta property="og:description" content="Descrizione pippo e pluto">
<meta property="og:url" content="www.mydomain.com">
<meta property="og:site_name" content="mydomain.com">
<meta property="og:image" content="http://mydomain.com/img/ar.png">


</head>


</html>
il debugger per open graph di facebook mi da quando una serie di errori del tipo

Inferred Property The 'og:url' property should be explicitly provided, even if a value can be inferred from other tags.
Inferred Property The 'og:title' property should be explicitly provided, even if a value can be inferred from other tags.
Inferred Property The 'og:description' property should be explicitly provided, even if a value can be inferred from other tags.
Inferred Property The 'og:image' property should be explicitly provided, even if a value can be inferred from other tags.
og:image could not be downloaded or is too small og:image was not defined, could not be downloaded or was not big enough. Please define a chosen image using the og:image metatag, and use an image that's at least 200x200px and is accessible from Facebook. Image 'http://www.miosito.it/admin/img/miaImage.jpg' will be used instead.
facendo un redirect a mydomain.com e pescando le info nella root.
Altre volte mi da errore del tipo:

Error parsing input URL, no data was cached, or no data was scraped.

in maniera arbitraria e senza una logica.

Eppure la pagina mi sembra ben strutturata e molto semplice.
Qualcuno può darmi una mano?