Error while invoking 3rd party web service

Local XmlDoc &IncRequest, &IncResponse, &xmldocReturn;

   Local string &return_data;

  

  

   Local XmlNode &EnvNode

  

   &IncRequest = CreateXmlDoc("");

   &EnvNode = &IncRequest.CreateDocumentElement("CreateChangeService");

   &EnvNode.AddElement("ServiceDeskEnvironment").NodeValue = "DEV";

   &EnvNode.AddElement("ServiceDeskUserID").NodeValue = "";

   &EnvNode.AddElement("ServiceDeskPassword").NodeValue = "";

--for all the parameters ....

...

Local Message &RESP_MSG;

  

      If %IntBroker.IsOperationActive(Operation.CreateChangeRequest, "V1") Then

      Local Message &ReqMsg = CreateMessage(Operation.CreateChangeRequest);   

     

      &ReqMsg.SetXmlDoc(&IncRequest);

      &RESP_MSG = &ReqMsg.SyncRequest(); 

      &xmldocReturn = &RESP_MSG.GetXmlDoc();

      &return_data = &xmldocReturn.GenXmlString();

     

   End-If;

I have written a code above to create a change request automatically by consuming a 3rd party web service.  Everytime I invoke the above code I get an error in the line       &RESP_MSG = &ReqMsg.SyncRequest();   . When I check the errorLogs it shows an error "Object reference not set to an instance of an object".  Can anyone help.