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);