problems once i use the progress bar

i have this code :
     
    define('_MPDF_URI','./classes/mpdf/');
    include_once('classes/mpdf/mpdf.php');

    $mpdf=new mPDF();
    $mpdf->SetDirectionality('rtl');
    $mpdf->autoLangToFont = true;
    $mpdf->debug = true;
   
    $mpdf->StartProgressBarOutput(1);

  
    ob_start();

    require_once("./emails/weekreport.php");


    $html = ob_get_contents();

    ob_end_clean();


    $mpdf->WriteHTML($html);

    $mpdf->Output();
    deleteFiles("/images/drealtimereport/");

if i am not using the progressbar and the _MPDF_URI part, the graphs images are being deleted, but one i use the progressbar the images are not being deleted.
any idea?