I had installed it some time ago and it was working fine. Now it's not anymore. Like other people have already reported here, I was getting the 500 error. It's not my server, as they (or I) have changed nothing. It's probably some policy change in Facebook. I know they changed quite a few things there about a month ago, and so maybe the plugin needs adjustment...
I'm not an expert on app developing for Facebook, but I had some other apps that were working there (I had them installed on my own page there) and now they aren't anymore.
I tried to re-install this connection plugin, but now all I get is an error message when I try to save the settings. (OBS: the App id and the App secret are correct, I triple checked that!)