Please try to disable whatever SEF extension you're using to see if that fixes the problem. If it's a 3rd party extension, like sh404SEF, please make sure to have it 'skip' altering URLs for JFBConnect. That's the most common cause of issues.
If that doesn't help, set the "Enable Debug Mode" setting in JFBConnect to 'Yes' and test again. Let us know if there are any more detailed error messages presented.
Thanks,
Alex