Fatal error: Uncaught Error: Class 'PHPExcel_Writer_Abstract' not found in /opt/lampp/htdocs/dhtmlxSuite_v5.1/codebase/grid-excel-php/lib/PHPExcel/Writer/Excel5.php:28 Stack trace: #0 {main} thrown in /opt/lampp/htdocs/dhtmlxSuite_v5.1/codebase/grid-excel-php/lib/PHPExcel/Writer/Excel5.php on line 28