Purchase Order Cancellation Functionality in R12

Hi,

I want to cancel a PO from PL/SQL package. I am using the API po_document_control_pub.control_document to cancel the PO but it is throwing the error code 'U' (UnExpected) with below error messages:

User-Defined Exception in Package po.plsql.PO_Document_Cancel_PVT. Procedure update_closed_code:002:1:User-Defined Exception

User-Defined Exception in Package PO_Document_Cancel_PVT Procedure cancel_document:004.

But from PO screen -> Tools -> Cancel option, i am able to cancel the PO.

Anybody has idea on what API, the PO screen is using for the PO Cancellation.

Thanks

Harikrishna