500 Error

Are you using a 3rd party SEF extension like sh404SEF, AceSEF, ArtioSEF, etc? If so, please go into that extensions's settings and set JFBConnect to not have SEF URLs. Each extension is different on how they allow you to 'skip' or use 'default Joomla URLs', but that's what you'll need to do.

If you aren't using a 3rd party SEF extension, please disable any profile plugins you have enabled and see if that improves the situation.

Let us know how that goes,
Alex