MPDF error requires mb_string functions

MPDF error requires mb_string functions. Make sure PHP is compiled with php_mbstring.dll enabled ????

code:

require_once("../mpdf/mpdf.php");

ob_start();

$template = ob_get_contents();

$template=$html;
ob_end_clean();

$mpdf=new mPDF(); 

$mpdf->WriteHTML($template);


$root = $_SERVER['DOCUMENT_ROOT'];
//$mpdf->Output($root.'/Dockets/'.$md5docketid.'.pdf', 'F');

//$mpdf->Output('C:\\'.$md5docketid.'.pdf', 'F');

$root = $_SERVER['DOCUMENT_ROOT'];
//echo $root;
$mpdf->Output($root.'/Dockets/'.$md5docketid.'.pdf', 'F');