delphi 2007 的问题

我做一个线程封装tidhttp来下载文件，原来在delphi7中编译都没问题，但是升级到delphi2007就出现了不能给tidhttp的事件付值的问题
procedure TDownThread.OnWork(ASender: TObject; AWorkMode: TWorkMode;AWorkCount: Integer);
begin
  if Assigned(FOnDownWork) then begin
    FOnDownWork(AWorkCount);
  end;
end;
procedure TDownThread.Execute;
begin
  FIdHttp.OnWork:=self.OnWork;
end;红色的提示：'tidhttp'does not contain a member named 'OnWork'请高手指教是什么问题呢