Error code 1111 in a orange box / orange line

[ Moved to Fixing WordPress from Requests and Feedback ]

Hello Everyone, I’m not really used to wordpress and I’m quite new to these kind of thing. A couple of days ago, a little box and an error code 1111 appeared in the HEAD of the site and it’s not even in a html tag. When I go in the console, there’s Vimeo links that can’t be loaded ( 6 of them ) and the error disappear if I erase this line :

wp_head();

In the Header.php …. Of course the wp_head() is really important, but is there someone out there that have a clue what might cause this error / strange bug? I’ve never done any back-end in that project, so would it be a plugin problem, a php update problem, or a wordpress version problem since I’m not using 4.7.3?

Because I didn’t update the php and three plug-ins,because the error is messing with my backup plug-in giving me the error :

Stats serveur: 404 – Not Found
Message d’erreur: 1111

I’ve been searching for some clues for about a week now without any success, because nobody seems to have ever experienced this error … or am I looking for the wrong thing?

Thank you in advance for your comprehension