SESSION problem

<?php session_start(); ?>
<!DOCTYPE html>
<html lang="da" dir="ltr">
<head>
  <?php
  $title = "Kontrolpanel | Min profil";
  $desc = "Gå til din profil på selvmægler | Boligsalg gjort hurtigt, nemt og simpelt";
  include('head.php'); ?>
</head>
<body>

  <?php
  //Menu box
  include('navigation.php');

  include_once("action/databaseconnection.php");
  if (isset($_SESSION['sess_user_id'])) {
    //Hvis personen er logget ind kommer denne.
    $ID = $_SESSION['sess_user_id'];

    //SQL sætning til databasen
    $query = "SELECT * FROM User
    WHERE UserID = $ID";

    //Variabel med array af resultaterne fra databasen
    $result = mysqli_query($con, $query);
    $row = mysqli_fetch_array($result);
     ?>

    <div class="min-container">

    <?php include('usermenu.php'); ?>
      <div class="output">
        <div class="opbox">
          <form class="" action="action/saveprofile" method="post">
            <div class="opheadline">
              <div class="ophdleft">
                <h1 class="ophleft">Min profil</h1>
              </div>
              <div class="ophdright">
                <button class="ophright" type="submit" name="button">Gem oplysninger</button>
              </div>
            </div>

          <div class="op">
            <div class="line1">
              <div class="opinput1">
                <h3 class="opibhead">Fornavn</h3>
                <? if ($_GET['frontname'] == "missing") {
                    ?>
                    <input type="text" class="invalid" name="firstname" value="<?php echo $row['FirstName']; ?>">
                    <?
                } else {
                    ?>
                    <input type="text" name="firstname" value="<?php echo $row['FirstName']; ?>">
                    <?
                }?>
              </div>
              <div class="opinput2">
                <h3 class="opibhead">Efternavn</h3>
                <? if ($_GET['lastname'] == "missing") {
                    ?>
                    <input type="text" class="invalid" name="lastname" value="<?php echo $row['LastName']; ?>">
                    <?
                } else {
                    ?>
                    <input type="text" name="lastname" value="<?php echo $row['LastName']; ?>">
                    <?
                }?>
              </div>
            </div>

            <div class="line1">
              <div class="opinput1">
                <h3 class="opibhead">Email</h3>
                <input type="email" name="email" value="<?php echo $row['Email']; ?>">
              </div>
              <div class="opinput2">
                <h3 class="opibhead">Telefon nr.</h3>
                <? if ($_GET['phone'] == "missing") {
                    ?>
                    <input type="tel" class="invalid" name="phone" value="<?php echo $row['Phone']; ?>">
                    <?
                } else {
                    ?>
                    <input type="tel" name="phone" value="<?php echo $row['Phone']; ?>">
                    <?
                }?>
              </div>
            </div>

            <div class="line1">
              <div class="opinput3">
                <h3 class="opibhead about">Om mig</h3>
                <textarea type="text" name="about" id="about" class="about"><?php echo $row['About']; ?></textarea>
              </div>
            </div>

            <div class="line1">
              <div class="opinput3">
                <h3 class="opibhead">Facebook link</h3>
                <input type="text" name="facebook" class="facebook" value="<?php echo $row['Facebook']; ?>">
              </div>
            </div>
          </form>
              <?php include('action/alert.php'); ?>
        <form class="" action="action/changepass" method="post">
          <div class="changepass">
            <div class="cpheaddiv">
              <div class="cphead">
                <p>Ændre adgangskode</p>
              </div>
              <div class="cpbutton">
                <button type="submit" name="button">Skift kode</button>
              </div>
            </div>
            <div class="passchange">
              <div class="old">
                <h3 class="opibhead">Gammelt kodeord</h3>
                <input type="password" name="oldpass" value="">
              </div>
              <div class="newpass">
                <h3 class="opibhead">Nyt kodeord</h3>
                <input type="password" name="newpass" value="">
              </div>

            </div>
          </div>
          </form>


          </div>
      </div>
    </div>

  </div>

  <?php
  }
  else {
    require_once('action/databaseconnection.php');
    ?>
    <div class="fejl">
      <div class="fejlbox">
          BEMÆRK: Du skal være logget ind for at tilgå denne side.
      </div>
    </div>
    <?php
    include('loginpage.php');
    }
 ?>

 <script src="js/alert.js"></script>
<?php
$error = $_GET['NoMail'];
if($error=='tom'){echo '<script>error("Fejl. Du skal bruge en Email for at kunne logge ind.");</script>';}


$error = $_GET['Password'];
if($error=='wrong'){echo '<script>error("Koden er forkert. Indtast en anden.");</script>';}

$succes = $_GET['Billedeupload'];
if($succes=='success'){echo '<script>success("Dit billede blev uploadet.");</script>';}

$error = $_GET['Billedeupload'];
if($error=='toolarge'){echo '<script>error("Billedet er for stort. Må maks fylde 2mb.");</script>';}

$error = $_GET['Billedeupload'];
if($error=='filtypeforkert'){echo '<script>error("Upload venligst JPG eller PNG filer.");</script>';}

$error = $_GET['Billedeupload'];
if($error=='fejl'){echo '<script>error("Der skete en fejl. prøv igen.");</script>';}

$succes = $_GET['password'];
if($succes=='changed'){echo '<script>success("Din adgangskode blev opdateret.");</script>';}

$succes = $_GET['konto'];
if($succes=='oprettet'){echo '<script>success("Velkommen til! Udfyld dine informationer, så en potentiel køber kan kontakte dig.");</script>';}

?>
</body>
</html>