Hi Mahavir,
I'm sorry for the delay but what version of InfoPath and BizTalk are you using? Are you using the Human Workflow stuff? Why not just add a Web service data connection ot the form that calls biztalk and submits the form as a string? That will preserve the BizTalk PI (if there is one) and probably explains why it isn't working. Good luck!
Patrick Halstead
Project Manager at Qdabra