Sales order not getting delivered

Hi all,

One sales order has been created with three items. I have checked the Incompletion log , it is showing "Document Complete".

All the three line items have Delivery dates in the sales order.

But when creating delivery doc. it is showing "order cannot be delivered'.

it is that for every line item: "An item with no delivery quantity is not permitted. Item will be deleted."

what can be the problem?

thanks in advance,

sourav