เจอ Error Warning: Cannot modify header information - headers already sent by (output started at แก้ไขยังไง

<meta http-equiv="Content-Type" content="text/html; charset=windows-874">
<?
require 'common.inc' ;
$admin1="pu_admin";
$password1="16282827";
// Display error messages
function DisplayErrMsg( $message ) 
{
printf("<blockquote><blockquote><blockquote><h3><font color=\"#cc0000\">
        %s</font></h3></blockquote></blockquote></blockquote>\n", $message);
}

function authenticateUser($user, $password)
{
global $DB_SERVER, $HTTP__HOST, $DB_LOGIN, $DB_PASSWORD, $DB, $DOCROOT ;
// Open a persistent connection with the MySQl server
if (!($link = mysql_pconnect ($DB_SERVER,$DB_LOGIN, $DB_PASSWORD))) {
//   DisplayErrMsg(sprintf("internal error %d:%s\n",
 //     mysql_errno(), mysql_error()));
   DisplayErrMsg(sprintf("internal error %s %s %s %d:%s\n",$DB_SERVER, $DB_LOGIN, $DB_PASSWORD,
      mysql_errno(), mysql_error()));
   return 0 ;
}

// Do the user/password authentication
if (!($result = mysql_db_query("$DB", "select * from member where 
                user_id='$user'"))) {
   DisplayErrMsg(sprintf("internal error %d:%s\n", 
      mysql_errno(), mysql_error()));
   return 0 ;
}
if (($row = mysql_fetch_array($result)) && ($password == $row["password"] 
                 && $password != ""))
   return 1 ;
else
   return 0 ;
}
 ?>

<meta http-equiv="Content-Type" content="text/html; charset=windows-874">
<? ob_start() 
require	"functions.php" ;
//delete all the old cookies 
deleteCookies() ;
if (authenticateUser($form_user_id, $form_password))
{
   setcookie("cookie_passwd",$form_password);
   setcookie("cookie_user",$form_user_id);
   header("Location:http://$HTTP_HOST/$DOCROOT/member_complete.php"); //ถ้า login ผ่านให้มาหน้า meber_complete
   exit();
} else {
   header("Location:http://$HTTP_HOST/$DOCROOT/login_false.php");//ถ้า login ไม่ผ่านให้มาหน้า login_false
   exit() ;
}
function deleteCookies()
{
// delete all the old cookies 
for($i=0; $i<$total_items; $i++)
{
   setcookie("items_tray[$i]", "");
   setcookie("quantity[$i]", "");
}
setcookie("items_tray","");
setcookie("total_items","");
setcookie("quantity","") ;
}
ob_end_flush() ?>