SRW.USER_EXIST not working in PO Report

Hi,

I am running custom PO report and calling below statement from one of the program unit which works fine in 11.5.8 and throw error saying user exit failure in R12.

srw.user_exit('PO ARCHIVE_DOCUMENT DOCUMENT_TYPE="PO" 
                                          DOCUMENT_SUBTYPE=":poh_po_type"
                                          DOCUMENT_ID=":poh_po_header_id"
                                          PROCESS="PRINT"');

SRW INIT is already set in After Parameter Form Report trigger.

Could you please suggest?

Thanks,

Rajesh