JavaScript error on login

I'm not sure what JFile is doing trying to read that file. That's not something from JFBConnect. Do you have a compression / optimization extension running on your site that's trying to minimize Javascript files? If so, it sounds like it's acting a bit screwy.

I'd recommend disabling any compression stuff you have going on and see if that helps. Also, you can check to make sure that the following file loads, which may help narrow things down too:
components/com_jfbconnect/includes/jfbconnect.js

Thanks,
Alex