Be sure to read the Readme file if you are installing it for the first time. You have to enter your API key and secret code from Facebook. It won't work until all of the information is entered, so read the file.
Seems to be working on my 3.8.4 forum. New members still have to enter in some information, but it's better than nothing. I will keep it unless there are troubles down the road.
If you don't have an API Key, you need to go to Facebook
https://developers.facebook.com/apps/ and get one for your board.