未将对象引用设置到对象的实例
 string userName = Session["name"].ToString();
            DB.BLL.DBManager showsource = new DB.BLL.DBManager();
            DataSet ds = new DataSet();
            ds = showsource.ShowSource(userName);
            if (ds != null)
            {
                GridView1.DataSource = ds;
            }
 不懂怎么解决
------解决方案--------------------
Session["name"]为空
------解决方案--------------------
判断Session["name"]为空就不走下去啦
------解决方案--------------------

if(Session["name"] != null)

{

            string userName = Session["name"].ToString();

            DB.BLL.DBManager showsource = new DB.BLL.DBManager();

            DataSet ds = new DataSet();

            ds = showsource.ShowSource(userName);

            if (ds != null)

            {

                GridView1.DataSource = ds;

            }

}