Compatibility with Facebook Share Link?

I believe this is a problem with my forum board site.

If I'm trying to share a link from my forum board to my site, the link info/link thumbnail looks weird. No page title, no description, no thumbnail-nothing at all, only bad-looking link. Here's an screenshot:

http://i.stack.imgur.com/TEUg8.png

That's not the way it's supposed to show, right? Oddly, if I share a link from my main homepage (not from the forum board), it will display correctly. Like this one:

http://i.stack.imgur.com/2ekL3.png

The most weird thing is that only happens in my forum board. It's perfectly normal on my main site. Why does this happen? I once read meta tags and meta description affect this stuff, but my meta tags and meta description are fine...

EDIT: I've just remembered. A few months ago (about early 2011) there's nothing wrong with my forum boards (the description appears properly). It's only recently (about March 2011) it starts to behave weirdly.

FB's share mechanism pulls a lot of data from your meta tags. Make sure they're set right, e.g.,

<meta name="description" content="your_site_description_here">

FB also follows the opengraph protocol, so you can use that to set the images, etc that show up on the share window. (http://developers.facebook.com/docs/opengraph/), ex:

<meta property="og:image" content="/your/site/image.jpg">

would make whatever image is at your/site/image.jpg show up when you hit the share button for that page.

EDIT:

On further investigation, the FB linter shows that your site returns a 403 forbidden, which means that it's filtering out FB's spider for not being in an approved IP list, or something similar. This URL may contain some helpful info: (http://www.invisionmodding.com/topic/47252-how-to-let-facebook-spider-to-visite-my-forum/)