This happened when swapping out an image and deleting some text on a page. Using WPMobile Pro theme. First time ever that I've run into this...
Worked around by deactivating WP SEO, publishing then re-activating.
Warning: Division by zero in
/home/________/public_html/m/wp-content/plugins/wordpress-seo/admin/class-metabox.php on line 1273
Warning: Cannot modify header information - headers already sent by (output started at
/home/________/public_html/m/wp-includes/pluggable.php on line 866