In register.php find:
$user_showemail = (isset($HTTP_POST_VARS['user_showemail'])) ? intval($HTTP_POST_VARS['user_showemail']) : 0;
Replace it with:
$user_showemail = (isset($HTTP_POST_VARS['user_showemail'])) ? intval($HTTP_POST_VARS['user_showemail']) : 1;