This error first stems from the below post.
The issue is that whilst I thought the PDF might be causing the error, it appears that changing the preferred template to any of the other Packing Slip templates I have, or even the standard one still causes the same error. I also tested changing the preferred Invoice template incase I'm targeting the wrong template.
I've also tried to print various Item Fulfilments which all throw the same Unexpected Error.
I'm not sure what else could be causing the problem? I want to print a PDF of the Item Fulfilment but it appears that it isn't due to a workflow, which PDF I chose or which Item Fulfilment I use.
Can anyone else offer suggestions? I've filed a report to support in the mean time.
Thank you all~