implement a method of callback

i need implement a method of callback but i'm having problems in way like am implementing. Can someone help me?

procedure TfrmPrincipal.EnviarArquivo;
var
  intf: IDispatch;
  ftp2: OleVariant;
begin
  try
    intf := CreateOleObject('Chilkat95_0.Ftp2');
    ftp2 := intf;
    try

  // Callback
  ftp2.onProgressInfo := ftp_onProgressInfo;

  if ftp2.unlockComponent('unlocked') <> 1 then
    raise Exception.Create(ftp2.LastErrorText);

  ftp2.HostName := edtHostName.Text;
  ftp2.UserName := edtUserName.Text;
  ftp2.PassWord := edtPassWord.Text;
  ftp2.Port     := StrToInt(edtPort.Text);
  ftp2.Passive  := 1;

  if ftp2.Connect <> 1 then
    raise Exception.Create(ftp2.LastErrorText);

  if (ftp2.ChangeRemoteDir('IN') <> 1) then
    raise Exception.Create(ftp2.LastErrorText);

  if (ftp2.PutFile(odlgArquivo.FileName,
                  ExtractFileName(odlgArquivo.FileName)) <> 1) then
    raise Exception.Create(ftp2.LastErrorText);

  mmLog.Lines.Add('File sent!!!')
except
  on e:exception do
    mmLog.Lines.Add(e.Message);
end;

finally
    VarClear(ftp2);
  end;
end;