ฟ้อง eror แบบนี้ -แก้ไงครับ Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by

<?
session_start();
echo '<meta http-equiv="content-type" content="text/html; charset=utf-8"/>';
$username = $_POST['username'];
$password = $_POST['password'];
if ($username=="")
{ 
	echo"คุณยังไม่ได้กรอกชื่อผู้ใช้งาน";}
else if ($password=="")
{ echo "คุณยังไม่ได้กรอกรหัสผ่าน";}
else{
	include("connect.php");
	mysql_select_db("documentupload");
	$check_log = mysql_query("SELECT * FROM member WHERE Username='$username' and Password='$password'");
$objResult = mysql_fetch_array($check_log);
$num = mysql_num_rows($check_log);
if($num<=0)
{
	echo "UsernameหรือPassword อาจผิดพลาด";
}
else
	{
	echo "id : ".$_SESSION['ses_userid'] = session_id();
echo "<br> username : ".$_SESSION["ses_username"] = $objResult["Username"];
echo "<br> password : ".$_SESSION["Status"] = $objResult["Status"];
session_write_close();
if( $objResult["Status"]=="ADMIN")
		{
	//echo '<meta http-equiv= "refresh" content="4; url=PageUploadToMySQL1.php"/>';
	}
elseif($objResult["Status"]=="USER")
		{
echo '<meta http-equiv= "refresh" content="0; url=PageUploadToMySQL3.php"/>';
	}

}
}

?>