ulitimate facebook settings error: "An error occurred. Please try again later."

Hi all,
I had Ultimate Facebook running fine. Reinstalled WP on our server and went to setup Ultimate Facebook again.
It installs fine, but when I go to set up the plugin, I create the app, following the instructions, enter the API key, Application Secret, and Application ID - save changes, and then go to grant extended permissions.
However I receive the following error in the FB pop-up box:
"An error occurred. Please try again later."

Any ideas on what is going wrong here? I have tried multiple times with multiple new versions of the FB app.

thanks