This is a common error, and it usually indicates that a wrong .zip file was selected for upload during the theme installation.
To upload correct .zip archive, please do the following:
- Save the downloaded ThemeForest .zip archive (e.g. themeforest-17143566-airpro-heating-air-conditioninghvac-onepage-wordpress-theme-for-individuals.zip) to your disk
- unpack the archive
- in WordPress admin dashboard, go to Appearance => Themes => “Add New” dialog
- browse to the unpacked archive and select airpro-1.0.0-installable.zip
This should now correctly install the theme.
The process has been illustrated in this video instruction.