The response I gave there is exactly what I'd still recommend. We have many, many users on the latest release of JFBConnect and Joomla 2.5. We haven't determined any cause that the installation would fail, but the steps there should help re-install it so that all the files are properly loaded on your system.
Please follow those instructions, and if it doesn't work, let us know where you get stuck or if there is any different behavior. Also, let us know when you get the error (front-end or back-end, only when trying to authenticate, etc).