How to show the data of a logged in user

Good, some way to show the data of a logged in user?

I need that after a user logs in, in another page show me the data of this user:

I have two tables:

And this is my code with which I am validating and trying to extract the user's data.

<?php 
require_once('conexion.php');
session_start();

if (isset($_POST["submit"])) {

    $usuario=$_POST["nusuario"];
    $contrasena=$_POST["ncontrasena"];
    $usuario = stripslashes($usuario);
    $usuario = mysql_real_escape_string($usuario);
    $contrasena = stripslashes($contrasena);
    $contrasena = mysql_real_escape_string($contrasena);
    $id_emp="";

    $sql="SELECT * FROM usuario WHERE usuario='$usuario' AND (contrasena='$contrasena' AND estado='Activo') ";

    $result = $conn->query($sql);
    if ($result->num_rows == 1) {

          while($row = $result->fetch_assoc()) {
            $id_emp=$row["id_empleado"];

          }
            $_SESSION['iduser']=$usuario;

          $sql2="SELECT * FROM empleado WHERE id_empleado='$id_emp'";
          $result2=$conn->query($sql2);
          if ($result2->num_rows == 1) {
            while($row = $result->fetch_assoc()) {
                $_SESSION["nombre"]=$row["nombre"];
                $_SESSION["apellidos"]=$row["apellidos"];
                $_SESSION["tipo"]=$row["tipo"];
                $_SESSION["dni"]=$row["dni"];
                $_SESSION["ubicacion"]=$row["ubicacion"];
                $_SESSION["telfmovil"]=$row["telfmovil"];
                $_SESSION["email"]=$row["imagen"];

            }


            // header("Location: ../venta_venta.php");
          }


        // if($row = mysql_fetch_array($execute)){
        // }


            // $_SESSION['username'] = $username;


            $mensaje = "¡Bienvenido al Sistema!";
            echo "<script type='text/javascript'>alert('$mensaje');</script>";
            header( "refresh:0.2;url=../venta_venta.php" );
    }else{

        $mensaje = "Error! La contraseña o usuario ingresado son incorrectos";
        echo "<script type='text/javascript'>alert('$mensaje');</script>";
        header( "refresh:0.2;url=../login_agro.php" );

    }

}

$conn->close();

?>

As you can see in the code, I extract the data from my used table and store it in those variables $ _SESSION []. But now I want to show those values stored on another page called mantencion_cuenta:

<?php 
require_once('verifica.php');

?>

      <div class="form-group">
        <label for="idnombre">Nombre:</label>
        <input type="text" REQUIRED disabled class="form-control" id="idnombre" value="<?php echo $_SESSION['nombre']; ?>">
      </div>

And the error that you send me is the following:

<br /><b>Notice</b>:  Undefined index: nombre in <b>C:\xampp\htdocs\PROYECTO_WEB\mantenimiento_cuenta.php</b> on line <b>178</b><br />

And I do not understand why. Any idea how to fix it? Thanks in advance.