Unable to stream pdf: headers already sent problem in dompdf [closed]

Question

I have used dompdf to display the user information in admin of my wordpress project. While generating the PDF file it works perfectly in my local server. But in live server Unable to stream pdf: headers already sent message is displayed.

The page where pdf is generated is http://mysite.com/wp-admin/admin.php?page=certificate&id=4.

The file for this link is include(ABSPATH."wp-content/themes/ncc/certificate.php");

Here is the code I have used

<?php
require_once("dompdf/dompdf_config.inc.php");
ob_end_clean();
ob_start();
?>
<style type="text/css">
.fnt_italic { 
    font-size: 18px;
    font-style: italic;
    font-weight:bold;
    font-family:Arial, Helvetica, sans-serif;
}
.clsTd {
    font-size: 12px;
    /*font-family:"Courier New", Courier, monospace!important;*/
}
.clsBg {
    background-color:#000;
}
.clsBgGray {
    background-color:#CCCCCC;
}
.clsBgWhite {
    background-color:#FFF;
}
.clsBold {
    font-weight: bold;
}
.tbl { border:1px double #000000; }
.notes { font-size:10px; color:#999999; }
.clsDiv { padding-top: 20px; }
</style>
<div class="clsDiv">
<table align="center" cellpadding="6" cellspacing="2" width="90%" class="tbl">
  <tr>
    <td>
      <table border="0" cellpadding="6" cellspacing="2" width="90%" align="center">
         <tbody>
          <tr align="center">
            <td class="fnt_italic" colspan="2">Certificate</td>
          </tr>
          <tr align="center">
            <td colspan="2">Name</td>
          </tr>
          <tr align="center">
            <td colspan="2" class="clsTd">Email id</td>
          </tr>
         </tbody>
       </table>
     </td>
    </tr>
</table>       
</div>
<script type="text/php">
if ( isset($pdf) ) {

  $font = Font_Metrics::get_font("helvetica");
  $size = 9;
  $text_height = Font_Metrics::get_font_height($font, $size);

  $foot = $pdf->open_object();
  $w = $pdf->get_width();
  $h = $pdf->get_height();
  $y = $h - $text_height - 40;
  $pdf->close_object();
  $pdf->add_object($foot, "all");
  $color = array(0,0,255);
  $text2 = "Page: {PAGE_NUM} of {PAGE_COUNT}";
  $pdf->page_text(710, $y, $text2, $font, $size, $color);
  $text = "Text"; 
  $pdf->page_text(15, $y, $text, $font, $size, $color);
}
</script>
<?php
$data = ob_get_clean();
$old_limit = ini_set("memory_limit", "64M");
$dompdf = new DOMPDF();
$size = array(0,0,800.00,700.00);
$dompdf->load_html($data);
$dompdf->set_paper($size);
$dompdf->render();
$dompdf->stream('certificate.pdf');
?>

Can anyone help me what is the creating problem here. Thanks in advance