Drop ship PO not getting cancelled

Hi,

We want to cancel the drop ship PO,as Po line is of 100 qty but receiving is done for 95 qty. we want to cancell the 5 qty and close the po.

But when i tried to 'Finally close' the PO it shows me an error as below-

Error:

Cannot Finally Close the PO/Release as there are open sales order lines.

Also Find attached screen shot of the error MSG.

Regards,

Nisha Shahi