Fatal error: Class 'Drupal\excel_reports\Exception' not found in /usr/www/users/****/sites/all/modules/excel_reports/src/ExcelReport.php on line 24

I have tried to follow very vague installation instructions and I am not sure if I have named the library correctly but I have used PHPExcel or should it be PHPOffice. I have also named my path http://mydomain.com/active_contributors_export/xls and attached the Excel reports view to the page.

When I click on the XLS button on the views page I get a white page with the following error:

Fatal error: Class 'Drupal\excel_reports\Exception' not found in /usr/www/users/edgedwahvu/sites/all/modules/excel_reports/src/ExcelReport.php on line 24