PHP mail() function not sending email

I am attempting to send an email using the mail() PHP function. I had it working until I attempted to give it a subject of "User registration", then the mail is not sent!

Heres the code (have simplified it greatly)

$to = $this->post_data['register-email'];
$message = 'Hello etc';
$headers = 'From: noreply@example.com' . "\r\n" ;
$headers .= 'Content-type: text/html; chareset=iso-8859-1\r\n';
$headers .= 'From: Website ';
mail($to, 'User Registration', $message, $headers);

I also attempted to use a variable containing the string of text but that didnt work.

Why is it not sending the mail when I add the subject exception?

Thanks

EDIT: updated code thats still not working

$to = $this->post_data['register-email'];
$message = 'Hello etc';


$headers  = 'MIME-Version: 1.0' . "\r\n";
$headers .= "Content-type: text/html; charset=iso-8859-1\r\n";
$headers .= 'From: Website ';
mail($to, 'User Registration', $message, $headers);