No down payments are available fr active items

Hi experts;

     A down payment has been done for a vendor with Sp. G/L 2.

     At the time of invoicing the vendor a message appears informs that there is a down payment existing on the purchase order.

     Then press ENTER and a message says that ((Item is relevant to retention)).

     Then press ENTER and a message says that ((Special G/L transactions exist for indicator 2 and 3))

     Then when I select the Down Payment Clearing an error message appears says ((No Down Payments are available for active items))

However the total down payment for the vendor for that PO is greater than the amount of the invoice.

So can kindly some one help to understand the system behavior why it does not clear the invoiced amount against the down payment amount?

Thanks in advance;

Kind regards;

Ahmad Mahmud;