Thanks Murali for the response.
Here requirement is to just sent mail to SAP user's business workplace rather than a work item, hence I was using a mail step for sending the notification.
As this was not working, I created an activity step and a method which uses FM SWN_CREATE_SHORTCUT to generate shortcut to VA42 and send this link as attachment to user's business workplace using 'SO_NEW_DOCUMENT_ATT_SEND_API1'. Outcome is some junk value instead of call to VA42.