Honestly, I've been sitting here reading directions and tutorials, and user forum questions and this problem just does not click for me as easily. What seems to be tripping me up is the section in the plugin settings "Facebook User Account ID:" being referred to as admin ID. I've done what you have suggested and placed "100004270051146, 849734640" in the User Account ID section and I'm receiving the same error.
Object Invalid Value: Object at URL 'http://www.gorgeousunderground.com/2012/10/14/ep-305-versus-final-loveless-grey-dance-sexy-house/' of type 'article' is invalid because the given value 'gorgeousunderground' for property 'fb:admins' could not be parsed as type 'fbid'.
I'm also wondering if I should go through the steps of creating a Facebook app to connect our FB page to WordPress so others will have an easier time liking and sharing WP blog posts that will pull photos and not just the moderators that are linked through this plugin. Am I missing something here?