Are you using a separate extension for 3rd party URLs or are you using the built-in Joomla SEF support? If you're using something different, can you try to disable it temporarily to see if that fixes the issue?
I'm not sure why you'd be getting a 500 error otherwise if there isn't something intercepting the URL we're redirecting to and throwing that error. The URL itself is correct, so we'd need to narrow down why Joomla is not accepting it properly.
The other option is to try and disable all Social Profile plugins you have enabled to see if that fixes the issue. If so, we can help narrow down what's going wrong there.
Thanks,
Alex
Facebook login redirect to 500 Error
