Fatal Error when upgrading to WP 4

I’m trying to upgrade a site for a new client. It’s quite old, so the first thing I did was attempt to upgrade to 4.0. I got the main part of the site done just fine, but apparently the blog is in a separate directory. Sadly, I did not even consider this when I started work on the site. When I attempted to update the blog, I get this error:

Fatal error: Call to undefined function like_escape() in /homepages/9/d135772340/htdocs/blog/wp-includes/user.php on line 915

You can see the blog here:
https://www.bfitandwell.com/blog/

Note there are no menus like there are on the main site:
https://www.bfitandwell.com/

They disappeared when the site was upgraded.

A cursory search doesn’t unearth any results and this is a new one on me. Anyone who can tell me how to fix this?

Thanks!