If you are running B1UP 2016.10 or 2016.11 and use B1 Print and Delivery Dunning Wizard you will see that if you run a wizard and at the end execute any of the B1 Print and Delivery actions, the action will complete but you will see an error message (Could not find item on form error message)
This issue have been fixed in B1UP 2016.11 HF1 (http://www.boyum-it.com/sbo)
NB: The error itself is not dangerous to the system (but of cause annoying)