MercatorWebService40.MercatorWebServiceSoapClient client = new MercatorWebService40.MercatorWebServiceSoapClient();
MercatorWebService40.SecurityInfo si = new MercatorWebService40.SecurityInfo();
si.SecureKey = ... ;
MercatorWebService40.DataSetMws ds = client.Zselect(si, "select top 1 * from cli");
if (!string.IsNullOrEmpty(ds.LastError))
{
    MessageBox.Show("Zselect : " + ds.LastError);
    return;
}
DataTable dt_cli1 = ds.Value.Tables[0];