Customizing inventory templates- help to insert fields

Customizing inventory templates- help to insert fields

-Im trying to customize our sales orders but cant get the code to work- 
- ive made a new custom field with autonumber to replace the SO number in the Sales Orders, but cant get this to display with the code: 
Ordrenummer: ${SalesOrders.Ordrenummer } (.name of custom field)

-Also id like to have the subject line of the sales order stated on the order, but i cant get this done either
(this is placed in the header directly below the Sales Order title): 
Subject: $ {SalesOrders.Subject}

What am i doing wrong?