Molongui Authorship plugin issue

Hi,
I have just recently applied this theme to our site and its really clean and great.
But I have wanted to use this Molongui Authorship plugin, but an issue occurs where when the guest authors aspect of the plugin is activated and I make a guest author the author of a post, the post simply displays “by “, and not the guest author. This plugin does work if I was to use a wordpress user. If you would be able to help in any way that would be great, thanks!

William