after registering the user attempts to log in and then get this error message error 404
Hey there,
Hope you are doing great! 
To debug this issue further and confirm the cause, could you please confirm whether the issue persists if other plugins on your site have been disabled?
You can also try once re-saving permalinks : http://docs.rtcamp.com/rtmedia/troubleshooting/solve-404-page-not-found-error-media-tab-buddypress.html
Thanks, Archana