รบกวนทีนะคะ เกี่ยวกับ session ค่ะ Warning: session_start() [function.session-start]: Cannot send session cache limiter

<?php
session_start();
//ob_start();
$_SESSION[sess_userid] = session_id(); 
$_SESSION["usergig"] = $row["usergig"];
$_SESSION["passgig"] = $row["passgig"];
header("Location: index.php");
}
?>

<?php
session_start();
$usergig = $_SESSION[usergig];
if(empty($usergig)){
$showuser = "
<table width=100% border=0 cellspacing=1 cellpadding=1>
<form method=post action=signin.php><tr> 
<td><div align=center>ชื่อเข้าระบบ <input name=usergig type=text id=usergig size=10>
รหัสผ่าน <input name=passgig type=password id=passgig size=10>
<input name=submit type=submit value=เข้าระบบ!>
<a href=http://www.gigza.net/member/forget_password.php>ลืมรหัส?</a></div></td>
</tr></form></table>
";
}else{
$host="localhost";
 $username = "xxxx";
$password = "gigza";
$db="xxxx";
$connect=mysql_connect($host,$username,$password) or die ("Cannot Connect to MySQL");
mysql_select_db($db) or die ("Cannot connect to Database");
$sql="select * from member where usergig='$usergig'";
$db_query=mysql_db_query($db,$sql);
$result=mysql_fetch_array($db_query);
$id=$result[id];
$name=$result[name];
$showuser = "ชื่อผู้ใช้ระบบ : $name [ <a href=logout.php>ออกจากระบบ </a>]";
}
?>