Testing via a ESB, adding name space?

I'm trying to do a proof of concept around using SoapUI within our orgnisation. We have a REST service that simply returns a reference number so should be very easy to test.

This works in Fiddler, request body below, but how do I get this to work in SoapUI? I've added the blue parts of the body as parameters but I get 'Object reference not set to an instance of an object.' which according to the developer (who's too busy to help at the moment) is because all our services are behind a service bus. Would adding the namespace help - and if so how do I do that?

Thanks

D

<?xml version="1.0" encoding="utf-8"?><GetWorkReferenceIdRequest xmlns="http://xxxxxxx">
  <MessageHeader xmlns="http://xxxxxxxx">
    <MessageId>1234</MessageId>
    <InitiatorId>122343</InitiatorId>
    <ServerName>12123</ServerName>
    <BusinessProcessName>123</BusinessProcessName>
    <BusinessProcessId>123</BusinessProcessId>
    <DateTimeStamp>0001-01-01T00:00:00</DateTimeStamp>
    <ProcessHeader>
      <MessageStatus>Success</MessageStatus>
      <Details>
      </Details>
    </ProcessHeader>
  </MessageHeader>
</GetWorkReferenceIdRequest>