Forbidden error

When creating a snipet, and then try to save, I get an forbidden Error. In the error there is no reason at all why the error happen.

You can reproduce this by trying to insert this piece of code at HTML/PHP.

<?php 

/* Attempt MySQL server connection. Assuming you are running MySQL server with default setting (user 'root' with no password) */ 

$link = mysqli_connect("localhost", "root", "", "demo"); 

// Check connection 
if($link === false){ die("ERROR: Could not connect. " . mysqli_connect_error()); } 

// Attempt select query execution 
$sql = "SELECT * FROM persons";

?>