TeeChart web控件使用时Session失效错误的解决办法

try
    {
     tmp = (MemoryStream)Session["ch1"];
     tmp.Position = 0;
     ch1.Import.Template.Load(tmp);
    }
    catch(System.Exception ex)
    {
          tmp = new MemoryStream();//重新生成Stream
     ch1.Export.Template.Save(tmp);
     Session.Add("ch1",tmp);
         }