The method or operation is not implemented error

Question

Hi,
I am trying to call wcf having following function
[OperationContract]
public IEnumerable<string> GetFieldValues(FieldType field)
{
switch (field)
{
case FieldType.Source:
return new List<string>() { "SQL Server", "BizTalk Server", "MSIInstaller", "ADV", "SQLAgent" };
case FieldType.EventId:
return new List<string>() { "10115", "20988", "23434", "12323", "890099" };
default:
throw new Exception("Unknown type");
}
}
public enum FieldType
{ Source,EventId }
 
I have two comboboxes. If I select item from combobox1 and call wcf then according to selection items should be display in combobox2.I am calling as below:
ServiceReference1.WCFServiceClient client = new ServiceReference1.WCFServiceClient();
client.GetFieldValuesCompleted += new EventHandler<ServiceReference1.GetFieldValuesCompletedEventArgs>(client_GetFie
FieldNameList fl = (FieldNameList)Enum.Parse(typeof(FieldNameList), this.FieldName.SelectedItem.ToString(), false);
client.GetFieldValuesAsync(fl);
Exception come at red word that "The method or operation is not implemented."
how to resolve that?