Fatal error: Call to undefined function wp()

I want to restore a site. I get: Open Base Dir FAILED open_basedir is enabled. Issues can occur when this directive is enabled, and we recommend to disable this value in your php.ini file.
I have restored my website maindomain.com after upgrading to PHP 7. But I get this message: Fatal error: Call to undefined function wp() in /home/maindomainadm/domains/maindomain.com/public_html/wp-blog-header.php on line 16