Set value to Element in a message using xpath

Am trying to set value of a element in messageAssignment shape using xpath

xpath(IntegrationOrder,
“//*[local-name()=’IntegrationOrderInfo’][1]/*[local-name()=’IntegrationOrderId’][1]”) = TransmissionId

IntegrationOrderId is lnt64
TransmissionId = Int64
Everything is minoccurs = 0 maxoccurs =1

Getting the following error

selected a node which is not valid for property or distinguished field
retrieval, or it selected no node at all. Only text-only elements or
attributes may be selected.
       
Exception type: XPathSelectionException
Source: Microsoft.XLANGs.Engine
Target Site: Void XPathStore(System.Object, System.String)
The following is a stack trace that identifies the location where the
exception occured

   at Microsoft.XLANGs.Core.Part.XPathStore(Object rValue, String xpath)
   at testbits.test.segment2(StopConditions stopOn)
   at Microsoft.XLANGs.Core.SegmentScheduler.RunASegment(Segment s,
StopConditions stopCond, Exception& exp)

—
Thanks