No thumbnail displayed on Facebook post

Hello,

I have a problem with the plugin. I connected it to my facebook page and everything works fine, except the thumbnail.
When I publish a post on my WordPress blog, it also gets posted on my Facebook page, but the thumbnail is unfortunately not displayed. I chose as a post pictuer the picture from my wodpress media. On my WordPress blog, this picture is displayed, but on the Facebook page I only get the standart WordPress thumbnail (that looks like this: http://joshhighland.com.s3.amazonaws.com/blog/wp-content/uploads/2009/09/create-wordpress-thumbnails-300×300.jpg)

Do I have to add something more or change in order to get the right thumbnail displayed?

Thanks for your help!
Colin

http://wordpress.org/plugins/add-link-to-facebook/