สอบถามเกี่ยวกับ error ของ session ทีครับผม ว่าต้องทำการแก้ไขยังไงดีครับ

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/samsurin/public_html/onlineorder.php:2)

Warning: Cannot modify header information - headers already sent by (output started at /home/samsurin/public_html/onlineorder.php:2)

<meta http-equiv="Content-Type" content="text/html; charset=TIS-620"> 
<?
ob_start();
session_start();
include('connect2.php');
if(!isset($_SESSION["intLine"]))
{

	 $_SESSION["intLine"] = 0;
	 $_SESSION["strproductid"][0] = $_GET["productid"];
	 $_SESSION["strqty"][0] = 1;

	 header("location:show.php");
}
else
{
	
	$key = array_search($_GET["productid"], $_SESSION["strproductid"]);
	if((string)$key != "")
	{
		 $_SESSION["strqty"][$key] = $_SESSION["strqty"][$key] + 1;
	}
	else
	{
		
		 $_SESSION["intLine"] = $_SESSION["intLine"] + 1;
		 $intNewLine = $_SESSION["intLine"];
		 $_SESSION["strproductid"][$intNewLine] = $_GET["productid"];
		 $_SESSION["strqty"][$intNewLine] = 1;
	}
	
	 header("location:show.php");

}
?>