templates

Can anyone help.

I am having problems getting one of my templates to print off the information. In template (inventory templates) I have a sales order that I print off when i've created a job. In the top left hand corner it says Sales Order. Below that it says order number, due date and invoice number. All of these fields i fill in before printing off the sales order. But when i print the only one that has any information in is the due date, all the others remain blank and i don't know how to fix it.

When creating the template it has the following information in the fields

Order Number:${SalesOrders. Order Number}
Due Date: ${SalesOrders.Due Date}
Invoice Number : ${SalesOrders. Invoice No}

is this correct or do i have something wrong. My invoice template works fine and has the following

Invoice Date: ${Invoices.Invoice Date}
Invoice Number : ${Invoices.Invoice No}

Any help would be appreciated.

Regards
Martin