JFBConnect: "An error occurred. Please try again later."

Not sure what's the issue either, from a quick look over the page. Everything seems ok, but it's not always easy to find the underlying issue.

If you could, please try to click the Login With Facebook button while logged into Facebook with a user that is an administrator of the Facebook application. That will change the generic "An error has occurred" message to one with more details of the specific error. Once you get that, let us know what it is, and hopefully we can help you further.

Thanks!

Ahh, good sleuthing. I missed that.

When I look at the scripts that are loading on your page, I see the Facebook Javascript API being loaded twice. Once, from us, is loading the //connect.facebook.net/en_GB/all.js file (en_GB is simply the language of your Joomla site), and the other is //connect.facebook.net/en_US/all.js. I can't see the en_US version being loaded as it's probably from a separate Javascript file being loaded first, but that's likely the issue.

Loading the Facebook API twice, especially if it's being initialized with no API key (which would cause the APP_ID value to be blank as you stated) is likely the problem. I don't know where the other load is coming from, but if you can try disabling any other Facebook extensions to narrow it down, that would help. I see the Wibiya toolbar at the bottom as one of the candidates, but there may be others.

Hopefully this helps get you started, and let us know what you find!