Auto Generate Purchase Orders Error

Hi,

We've recently moved to 4.5 and are trying out the automatic generation of purchase orders. Unfortunately we're seeing an error that's a little odd. The error log shows the sales order number, the item code, and then states that, "The item code is required." So I'm confused - it's showing me the item code, and then saying it needs the item code? If anybody can shine a light on this paradox, I would greatly appreciate it!