Did you find a solution? I am new but I think it is because there isn't anything in the source code that tells Facebook there is an image to select. I fixed this on one page of my site by adding a custom field with <link rel="image_src" href="http://www.mysite.com/wp-content/uploads/2011/02/03.jpg" />
but this didn't work on other pages (different images/links)
Can anyone tell me if I could do something similar in the header.php? I.e. My theme gives me the option to add music- I will never have that. Can I take out the code for music and replace it with something to identify an image that isn't visible on the page but has been uploaded to my site?
The tech support from my theme is not helpful at all. I'd really appreciate any suggestions! Thanks!