Hofmockel.org

Symptom: Event.module has icalendar(webcal) links that are unwanted.
solution: If using PHPtemplate engine - In template.php add
'. l('', $path, array('title' => t('Add this calendar to your iCalendar')), NULL, NULL, TRUE, TRUE) .'';
// return preg_replace("|http://|","webcal://", $ical_link);
}
?>
Change 'mytheme' to the name of your theme.
For other theme engines follow this reference URL
ref: http://drupal.org/node/30062#comment-77333