Get 404 error showing behind google banner ad in header

I have never had this happen before, but I had someone work on my site a couple of months ago. I can’t figure out how to make it go away, but a 404 error shows up behind my banner ad. See it at http://glutenfreerecipebox.com/. When I look at the view source code, it appears to be coming from the Yoast plugin, but I can’t find out where to change it. Any help would be appreciated.