PHPTemplate override error

Hi,

I'm trying to create a custom email to be sent when a user submits data to my form. I've placed the following in my themes template.php :

function phptemplate_webform_mail_message_18($form_values, $node, $sid, $cid) {
  return _phptemplate_callback('webform-mail-18', array('form_values' => $form_values, 'node' => $node, 'sid' => $sid, 'cid' => $cid));
}

The node is called 18 (clean urls is NOT enabled)

The template file is called webform-mail-18.tpl.php and placed in the active theme directory (same directory as the template.php).

When the email is sent it comes through like:

This is the template I'm using (same as the suggested one in the readme)

<?php /* Begin sample webform mail message file */ ?>
Company X Official Website Submission
Message was submitted <?php echo format_date(time(), 'small') ?>
From the IP address <?php echo $_SERVER['REMOTE_ADDR']; ?>
The user's favorite color is <?php echo $form_values['submitted_tree']['favorite_color'] ?>
The user's problem is below:
<?php echo $form_values['submitted_tree']['problem'] ?>
<?php /* End sample webform mail message file */ ?>

Any help would be greatly appreciated.

Mike