You are using Nginx as your web server. When uploading large files to the media library you get an “HTTP Error” message. When switching to the old fallback uploader you get “413 Request Entity Too Large”.
The file data being posted is too large for current Nginx (and possibly PHP) settings.
First of all you need to check you
php.ini file that it allows the large file to be posted. Check the
upload_max_filesize so both values are higher then the file you are trying to upload.
Then add or update the client_max_body_size setting in your
/etc/nginx/nginx.conf or server block to a value high enough:
Finally make sure to restart Nginx and possibly PHP if you are running PHP-FPM.