That "Illegal Access" usually means that the plugin was being used outside of the Zen Cart environment (the IS_ADMIN_FLAG definition is used for the determination). The only place in the Sales Report's distribution that the message is used is in /YOUR_ADMIN/includes/functions/extra_functions/stats_sales_report.php.
Unfortunately, the plugin has historically included multiple files of the same name, i.e. stats_sales_report.php. Make sure that you didn't "finger-check" and copy that extra_functions version of the file to the /YOUR_ADMIN directory.
Bookmarks