How to assign output to XMLDo***ent

Hi,
  I am trying to use multiple maps in single orchestration. My
Orchestration 
receives different input HL7 messages and converts in to xml and depending
on 
input schemas map is also working fine. My orchestration having only one 
sends ****t. I successfully bind xml do***ent in Receive shape, but in send

shape I am unable to bind the OutputMessage (XMLDo***ent). It shows error
“Un 
constructed message”. 

Please tell me how to assign maps output to OutputMessage (XMLDo***ent). 

satya.