If you are receiving "Failed - Network Error" when trying to download a file from a website that uses Sucuri Firewall and the same error happens in more than one computer/network, please disable or ask your hosting provider or web developer to disable zlib.output_compression in your PHP configuration.
Usually you can disable it by adding this line in your .htaccess file:
php_flag zlib.output_compression off
Or adding this line to your php.ini file:
zlib.output_compression = Off
If it still doesn't work, please open a General Support Request.