First of all, great little plugin! Couldn't have asked for more.
However I have only one tiny (and I mean tiny) ammend.
In the function yidp_content, where you return the link to login to wordpress, don't forget to close off the tag.
The return statement of the function should look like the following.
return '<p><a href="' . wp_login_url( get_permalink() ) .'">' . $yidp_message. '</a></p>';
I hope this helps!