Hi Konstantin,
For my requirement PO workflow was only getting triggered for changed version.
So i had to get the PO instance / PO GUID as following
CALL FUNCTION 'BBP_PD_PO_GETDETAIL'
EXPORTING
i_guid = iv_document_guid
i_with_itemdata = space
TABLES
e_version = lt_version.
READ TABLE lt_version INTO ls_version WITH KEY version_type = 'C'.
IF sy-subrc IS INITIAL.
lv_guid = ls_version-guid.
ELSE.
lv_guid = iv_document_guid.
ENDIF.
After this when i used the code provided by you it worked.
Thanks For your help.
Regards,
Ashish