That's a normal error on your home page as that page is usually showing many articles and JFBConnect doesn't know which one should be the 'main' one. The image, generally, shouldn't change. So, if you're showing a blog view on your home page, it's not right to set the image to first article.. otherwise, that image will change whenever you add new content.The 'og:image' property should be explicitly provided, even if a value can be inferred from other tags.
{SCOpenGraph image=http://site.com/link-to-homepage-image.jpg}
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