Hello SavecoAdm,
To me it looks as if the so-called inventory posting matrix / form is not completely setup. Can you please check your account setup in the following form "InventoryManagement-Setup-Posting-Posting" and there the sales order tab? There you will find all the transactions types mentioned above (order packing slip, order offset account packing slip, etc.) for which you need to setup specific accounts.
If you can identify some accounts in those sections then please check your item setup and verify if the item is covered by one of the posting lines setup in this form.
Hope it helps,
Ludwig