PHP在header(）之后丢失SESSION变量

使用header（）重定向后，我不断丢失SESSION变量。我尝试了在类似问题中找到的所有解决方案，比如每页顶部的session_start（）和header（）之后的exit（），但都不起作用。每次我在succlog.php页面中收到"id not set"。重定向到succlog.php非常有效。你能帮帮我吗？这是代码：

登录页面：

session_name("session1");
session_start();
     ..........
$qry = "SELECT * FROM `members` WHERE `usr` = '$username' AND `pass` = '" . md5($password) . "'";
$result = mysql_query($qry);
//Check whether the query was successful or not
if(mysql_num_rows($result) == 1) {
    while($row = mysql_fetch_assoc($result)) {
        $_SESSION['id'] = $row['id'];
        $_SESSION['usr'] = $username;
        session_write_close(); 
        header("location: succlog.php"); //Redirect
        exit();
    }
}

succlog.php:

   session_name("session1");
   session_start(); 
    ...........
   <?php 
  if(isset($_SESSION['id'])){
    echo "id".$_SESSION['id'];
  }
  else{
    echo "id not set";
  }
  ?>