import demo problem

Hi:
There is no problem when I firstly install FORTUNA theme and import demo content. Yesterday I deleted all the files in FTP and re-install WordPress. When I import demo content, it unsuccess. Then I follow the DOCS to use WordPress database reset plugin and delete all the files in wp-content/uploads. But it still unsuccess.

WP shows as following:

Sorry, there has been an error.
File is empty. Please upload something more substantial. This error could also be caused by uploads being disabled in your php.ini or by post_max_size being defined as smaller than upload_max_filesize in php.ini.

Please help me

Thanks!