Please help friends, I have an error in my code. Sometimes the error appears but sometimes it goes away. I have attached my code below

Question

The following is an image of the error display that appears:

This my code below :

<?php
include "inc/koneksi.php";
include "inc/konf.php";
include ("katalog/header.php");

$mod = $_GET['mod'];
switch($mod){
    case "catalog" :
    $view = "katalog/katalog.php";
    break;
    case "info" :
    $view = "katalog/info.php";
    break;
    case "help" :
    $view = "katalog/bantuan.php";
    break;
    case "user" :
    $view = "katalog/pengguna.php";
    break;
    case "about" :
    $view = "katalog/tentang.php";
    break;
}
 include $view;

if(empty($mod)){
include ("katalog/katalog.php");
}
include ("katalog/footer.php");
?>