Invalid orders cannot be printed if you use the latest version.
Created orders can be printed though. If you don't want that, you can edit the file "show" of the view "order" via the menu Display->Views and change the line:
<?php if(hikashop_level(1) && $this->config->get('print_invoice_frontend') && !in_array($this->element->order_status,array('refunded','cancelled'))){ ?>
to:
<?php if(hikashop_level(1) && $this->config->get('print_invoice_frontend') && !in_array($this->element->order_status,array('refunded','cancelled','created'))){ ?>