Gemma I have this issue too and I've done some investigating.
I know the cause but I cannot solve it.
Facebook is not picking up any Opengraph meta tags, hence it doesn't know any of the parameters (this can be seen in the debugger tool.
On your site, og: tags are visible in the source code, like this:
Code:
<meta property="fb:app_id" content="snipped" />
<meta property="og:title" content="TOTWO" />
<meta property="og:type" content="website" />
<meta property="og:description" content="TOTWO is a pairs game. Click on the cards to see what is behind them, and try to match all the pairs before the time runs out!
Have fun!" />
<meta property="og:url" content="http://www.forumbanter.com/arcade/game-873/" />
<meta property="og:image" content="http://www.forumbanter.com/images/arcade/totwo.jpg" />
But as far as I can see this mod doesn't add those. I'm wondering if you have something else running that adds those for you, or whether you've added them manually, but without them it won't work.
Now, beyond that, I have tried adding suitable tags into the v3ARCADE_PLAY template, but Facebook still doesn't pick them up! Although they are visible in the source, Facebook's debugger doesn't "see" them.
Oddly if, as a test, I put some manual tags in the v3ARCADE_MAIN template, Facebook DOES see them (though of course that's no use for this mod!)
Bit weird and I've spent hours trying to figure it out to no avail.
It's possible others haven't reported this, since unless you try clicking your own Facebook links (which most people probably won't do), they may not be aware it might not be working.