Mass print action of PDF's

Using the mass action print Invoice, shipping or creditmemo gives error.

Problem:
When trying to do the mass print action on the order grid screen, an error is thrown.
Error text: Page is attached to other documen. Use clone $page to get it context free.

Solution:
The most common reason for this, is that another 3. party module is extending the Mage_Adminhtml_Sales_OrderController and therefor the HTML2PDF module is not being run here.

So find the 3. party extension that also extends Mage_Adminhtml_Sales_OrderController, and add the code found in the file app/code/community/Ext4mage/Html2pdf/controllers/Admin/OrderController.php

Related product:
  HTML2PDF extension