Access denied on print e-mail for book pages

I changed from the forward module to print_mail and now get a lot of Access denied messages on book pages.
The URL is: www.example.com/printmail/book/export/html/[nid]
As far as I know in D5 is only one permission: access send to friend and this is enabled.

I tested it also in D6. There it works as expected.

I pathed my version:
In function _print_mail_access($permission)
In this part:

    if (is_numeric($parts[1])) {
      $path = 'node/'. $path;
    }
    else {
      $path = drupal_get_normal_path($path);
    }

I added 4 lines as follows:

    if (is_numeric($parts[1])) {
      $path = 'node/'. $path;
    }
    // my patch, in total 4 lines, this line included
    elseif (substr($path, 0, 16) == 'book/export/html') {
      return (user_access($permission));
    }
    else {
      $path = drupal_get_normal_path($path);
    }

I don't know if this is the correct fix, but for me it works.

Thank for a great module.