有些页面需要重新登录

Question

当我执行需要登录用户的操作时，我有时必须重新登录。大部分时间都是在我第一次登录时发生的。注销后，我无法重新创建该问题。

谁知道出了什么问题？

在索引页面的顶部，我有session_start（）; 在索引页面中，我已包含所有其他页面。

登录页面：

function login_form()
{
if($_SERVER['REQUEST_METHOD'] == 'POST') {

    $qLogin = mysql_query("SELECT G_id FROM users WHERE
                G_name  = '".mysql_real_escape_string($_POST['G_name'])."' AND
                password     = '".sha1($_POST['password'])."'");

    $qActivatie = mysql_query("SELECT COUNT(G_id) FROM users, user_activaties WHERE
        users.G_name    = '".mysql_real_escape_string($_POST['G_name'])."' AND
        users.G_id             = users_activaties.users_id");

    if(mysql_result($qActivatie,0) != 0) {
        echo 'account not activated.';
    } elseif(mysql_num_rows($qLogin) == 0) {
        echo 'user name/password is not correct.';
    } else {
        $_SESSION['user']         = mysql_result($qLogin, 0);
        $_SESSION['G_name'] = $_POST['G_name'];
         header("Location: index.php?func=panel ");
        ?>
        Succesfull logged in.<a href="controlpanel.php">Click</a> 
        <?php
    }
}
?>
         <div id="login">

    <form action="<?=htmlentities($_SERVER['REQUEST_URI'])?>" method="post">
        <input type="text" name="G_name" placeholder="User"/>
        <input type="password" name="Password" placeholder="Password"/>
    <button type="submit">Login</button>
        </form>
</div>
        <?php
    }

有时需要重新登录的操作

session_start();
include("db.php");

$O_id=$_GET['O_id'];
$G_id=$_GET['G_id'];
$G_name=$_GET['G_name'];
$aanwezig=$_GET['aanwezig'];

$query = mysql_query
("INSERT INTO koppeltabel(O_id, G_id, aanwezig)
VALUES ('$O_id','$G_id', '$aanwezig')
ON DUPLICATE KEY
UPDATE aanwezig='$aanwezig' ");
mysql_query($query);
header('Location: http://www.abc.nl/new/index.php?func=option');