Login Error: There is an error in logging you into this application.

Hi I have this plugin installed and functioning perfectly for several months until today. This is the website:https://www.seekmedi.com/
The Facebook button on the header was working fine, but now it opens a page with a line of error message: Login Error: There is an error in logging you into this application. Please try again later.

Please Help. Thank you.
This is the HTML code for the FB button:
<div class=”new-fb-btn new-fb-1 new-fb-default-anim” style=”margin:15px auto 0; position:absolute; left:0; right:0; width:140px;”>
<div class=”new-fb-1-1″>
<div class=”new-fb-1-1-1″>
LOG IN
</div>
</div>
</div>