delphi 调用c#写关于a+b的webservice，返回值不对？该如何处理

delphi 调用c#写关于a+b的webservice，返回值不对？
调用helloWorld的返回值是正确的，调用add的时候，传入（1，2）时，返回值却为0，不知什么原因，这个问题困惑了很久，请高手们指教~


以下是源码
//c#写的webservice的源码
[WebService(Namespace   =   "http://tempuri.org/ ")]
[WebServiceBinding(ConformsTo   =   WsiProfiles.BasicProfile1_1)]
public   class   servTest   :   System.Web.Services.WebService   {

        public   servTest   ()   {

                //Uncomment   the   following   line   if   using   designed   components  
                //InitializeComponent();  
        }

        [WebMethod]
        public   string   HelloWorld()   {
                return   "Hello   World ";
        }
        [WebMethod]
          public   int   add(int   a,   int   b)
        {
                return   a   +   b;
        }
}


//*****************************************
//**************************************
//wdsl导入的代码
//   ************************************************************************   //
//   The   types   declared   in   this   file   were   generated   from   data   read   from   the
//   WSDL   File   described   below:
//   WSDL           :   http://10.20.10.224/servTest.asmx?wsdl
//   Encoding   :   utf-8
//   Version     :   1.0
//   (2007-7-27   下午   04:48:35   -   1.33.2.5)
//   ************************************************************************   //

unit   servTest;

interface

uses   InvokeRegistry,   SOAPHTTPClient,   Types,   XSBuiltIns;

type

    //   ************************************************************************   //
    //   The   following   types,   referred   to   in   the   WSDL   document   are   not   being   represented
    //   in   this   file.   They   are   either   aliases[@]   of   other   types   represented   or   were   referred
    //   to   but   never[!]   declared   in   the   document.   The   types   from   the   latter   category
    //   typically   map   to   predefined/known   XML   or   Borland   types;   however,   they   could   also  
    //   indicate   incorrect   WSDL   documents   that   failed   to   declare   or   import   a   schema   type.
    //   ************************************************************************   //
    //   !:string                     -   "http://www.w3.org/2001/XMLSchema "
    //   !:int                           -   "http://www.w3.org/2001/XMLSchema "