problem importing demo content from wordpress theme

Hi, i have bought a theme from themeforest and have been asking questions on their support forum for days but did not get a reply.
I have been trying to import demo content from the theme itself but i always get this message:

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.

PLs advice me of what could have went wrong. Thanks!!