delphi点击外部程序的按钮

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Memo1: TMemo;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
  h, i: HWND;
  j, k : HWND;
  l, m : HWND;

begin
  h := FindWindow(nil, '搜狗拼音输入法 5.2正式版 安装');

  while(h<>0)  do
  begin

  i := FindWindowEx(h,0,'Button','下一步(&N) >');
  SendMessage(i, BM_CLICK, 0, 0);
  sleep(100);
  memo1.Lines.Add('action 1') ;


  j := FindWindowEx(h,0,'Button','我接受(&I)');
  SendMessage(j, BM_CLICK, 0, 0);
  sleep(500);
  memo1.Lines.Add('action 2') ;







  end;



end;

end.
这是代码，前几个按钮都能够正常点击，为什么最后一个不行？望高手赐教。。。