Sort undo error

I get an error when I try to execute a request to a SOAP service:

Unmarshalling Error: unexpected element (uri: "http://www.domain.com/ws/servicename/", local: "dummyArg"). Expected Elements: <{} dummyArg>

The method that I call is defined as:

function GetTxServer(UseWSDL: Boolean; Addr: string; HTTPRIO: THTTPRIO): TxServer;

I have little experience with SOAP, and I have not found any useful information about this. Feel free to ask any questions that might speed up the process of finding a problem.

I believe that the way I call a function is not the right way!

I am using Delphi 2010, and I called the method as follows:

Response := GetTxServer.requestIVULoto(cm);