500 - View not found - Selectively Unable To Login

We were able to fix the issue on the gratefuljoy website below. There was a bug in our code which was preventing the {fb_uid} tag from correctly being replaced in the username, and therefore was not always creating a unique username.

There are two options to try to fix this issue. Either you can attempt to change the code yourself if you'd like, or you can use a different combination in the username to try to fix this issue. If you aren't using {fb_uid}, unfortunately, this is not your issue (see the bottom for another thing to try to help diagnose the problem).

{fb_uid} Fix in code:
Line ~62 of components/com_jfbconnect/controller.php
Change the line to the following. The change is the middle parameter ($rawFbUserId) used to be $fbClient->user:
$username = str_replace("{fb_uid}", $rawFbUserId, $username);

Alternative debugging
If this is not your problem, can you also change the following to see if instead of the error page you are seeing, you instead get redirected to the home page with a more standard error:
Lines 81 and 91, remove JRoute::_() from the statement, leaving index.php:
$mainframe->redirect('index.php');

We are still investigating the foreign character issue.