Error While Posting since 4.6 upgrade

Try:
– switching to the default theme automatically by renaming your current theme’s folder inside wp-content/themes and adding “-old” to the end of the folder name using FTP or whatever file management application your host provides.

– resetting the plugins folder by FTP or phpMyAdmin.

– re-uploading all files & folders – except the wp-content folder and the wp-config.php & root .htaccess files – from a fresh download of WordPress. Make sure that you delete the old copies of files & folder before uploading the new ones.

– running the upgrade manually via wp-admin/upgrade.php