I'm using different pages on fb for my different websites. For some reason, I only got the last of all my fb pages as a possibility to choose from, when trying to connect my site with fb.
I could somehow change that by modifying the code in line 1104 of the file class-config.php in the admin folder from
$options['fbpages'][$page->page_id] = $page->name; into
$options['fbpages'][intval($page->page_id)] = $page->name;
I'm just not sure whether or not this can be a solution for everybody. It's not completely tested through all my sites yet.