If you receive this message when updating your theme, most likely you need to delete the header.php and footer.php from your child theme, and copy the same two files from the new parent theme. Sometimes major changes are done to those files, which can results in your child theme files needing updated. In the future, we are going to eliminate the need for this process.
Fatal Error: Call to a member function have_posts() on a non-object
Fatal Error: Call to a member function have_posts() on a non-object