XML : xml document must contain a root level element

In my bootstrap PHP-file there is an error that says: "xml document must contain a root level element"

Here is the code:

   <?php  // Check for empty fields  if(empty($_POST['name'])        ||     empty($_POST['email'])       ||     empty($_POST['phone'])       ||     empty($_POST['message']) ||     !filter_var($_POST['email'],FILTER_VALIDATE_EMAIL))     {      echo "No arguments Provided!";      return false;     }    $name = $_POST['name'];  $email_address = $_POST['email'];  $phone = $_POST['phone'];  $message = $_POST['message'];    // Create the email and send the message  $to = 'mymailaddress'; // Add your email address inbetween the '' replacing yourname@yourdomain.com - This is where the form will send a message to.  $email_subject = "Website Contact Form:  $name";  $email_body = "You have received a new message from your website contact form.\n\n"."Here are the details:\n\nName: $name\n\nEmail: $email_address\n\nPhone: $phone\n\nMessage:\n$message";  $headers = "From: noreply@yourdomain.com\n"; // This is the email address the generated message will be from. We recommend using something like noreply@yourdomain.com.  $headers .= "Reply-To: $email_address";   mail($to,$email_subject,$email_body,$headers);  return true;              ?>     

• Is this because Visual studio (where I'm editing) can't manage PHP?
• What can I do? What kind of root-element shall I add?

When I run the code the following error-message pop up on the webbsite: "Sorry, it seems that my mail server is not responding. Please try again later!"