I have set the following payment terms
   
Due 15th Of the Following Month    Day In Following Month    17       
Due By End Of The Following Month    Day In Following Month    30       
Payment due within 10 days    After No. of Days    10 days       
Cash Only    Cash    N/A       
Advance Payment    Prepayment    N/A       
To pay after 2 weeks    After No. of Days    14 days

But when I go to Sales > Direct Invoice, I cannot choose the payment terms to use. It just display one payment term that is set for that one customer. Initially I could select from a dropdown input filed but now I don't have any option. I don't know what got messed up.       

Where to I go to get the dropdown select box again to choose the payment terms while create a new Invoice?

Note:

I cannot select the payment also in

> Sales Quotation Entry
> Sales Order Entry
> Direct Sales Delivery