InfoPath Dev

I have a InfoPathe - code in c# .NET.
I have a Web Reference to SharePoint Web Service - GetListItems().

I operate this code:

XmlDocument xmlDoc = new System.Xml.XmlDocument();
XmlNode ndQuery = xmlDoc.CreateNode(XmlNodeType.Element,"Query","");
XmlNode ndViewFields = xmlDoc.CreateNode(XmlNodeType.Element,"ViewFields","");
XmlNode ndQueryOptions = xmlDoc.CreateNode(XmlNodeType.Element,"QueryOptions","");


string str=this.thisXDocument.DOM.selectSingleNod("//my:IDNumber").text;


ndQueryOptions.InnerXml= "<IncludeMandatoryColumns>FALSE</IncludeMandatoryColumns>" +
"<DateInUtc>TRUE</DateInUtc>";

ndViewFields.InnerXml = "<FieldRef Name='Fname' /><FieldRef Name='Lname'/>";

ndQuery.InnerXml="<Where><Eq><FieldRef Name='Fname'/><Value Type='String'>" + str +"</Value></Eq></Where>";

try
{

XmlNode returnXml = s.GetListItems("MyList",null,ndQuery,ndViewFields,null,ndQueryOptions);
this.thisXDocument.UI.Alert(returnXml.OuterXml);

}

catch (System.Web.Services.Protocols.SoapException ex)
{
this.thisXDocument.UI.Alert("Message:\n" + ex.Message + "\nDetail:\n" +
ex.Detail.InnerText +
"\nStackTrace:\n" + ex.StackTrace);
}

I get eroor of "Field with this name not exist"
What is the problem

This is not really an IP issue, I bet you would probably run into the problems if you were writing this .net code outside of IP. Suggest you do some reading up on how to call WSS Web Services. They are documented in the MSDN library.