On the home page of your site, there is no og:image tag specified. In the main article that you have on that page, if I click into it, I am able to see the og:image tag set properly.
Can you tell me what type of menu item you are using for your home page and how you are expecting the og:image tag to be set? From what I can gather, it's a blog or featured layout view. In that case, you'll need to either set an image for the category or use the JFBConnect Easy Tag to set the image for the page, like:
{SCOpenGraph image=http://yoursite.com/link-to-image.jpg}
Finally, you can also set a default image to be used on all pages of your site in the JFBConnect -> Social Meta area. That's great for a logo or something else generic that could work on any page if one can be set automatically.
I hope that helps with some ideas, but if not, or you think there is an issue with the home page menu item, let us know any more details you can so we can understand further.
Thanks,
Alex