AspNetPager控件做翻页，从其他页返回出错。

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {           
             string 条件= " from info where 1=1";        if (Request.Form["id"] != "")
        {........条件语句    }
        else
        {........条件语句    }
        string sqlStr = "select count(distinct(id)) as all_num " + 条件+"";        if (Request.QueryString["page"] == null)
        {
            Session["sqlString"] = sqlString;
        }
        else
        {
            sqlString = Session["sqlString"].ToString();
        }
            SqlConnection conn = new SqlConnection(strCon); ;  //新建数据库连接对象，其中s是上面的连接字符串
   
            conn.Open();    //打开与数据库的连接
            SqlCommand cmd = new SqlCommand(sqlStr, conn);
            AspNetPager1.AlwaysShow = true;
            AspNetPager1.PageSize = 2;
            AspNetPager1.RecordCount = (int)cmd.ExecuteScalar();
            conn.Close();
            bind();        }    }
     protected void AspNetPager1_PageChanged(object sender, EventArgs e)  
        {
            bind();
        }  
    //绑定
    public void bind()
    {
        string 条件= " from info where 1=1";        if (Request.Form["id"] != "")
        {........条件语句    }
        else
        {........条件语句    }
        if (Request.QueryString["page"] == null)
        {
            Session["sqlString"] = sqlString;
        }
        else
        {
            sqlString = Session["sqlString"].ToString();
        }
       
        string sqlstr = "select * " + 条件+"";        sqlcon = new SqlConnection(strCon);        SqlDataAdapter myda = new SqlDataAdapter(sqlstr, sqlcon);        DataSet myds = new DataSet();        sqlcon.Open();
        myda.Fill(myds, AspNetPager1.PageSize * (AspNetPager1.CurrentPageIndex - 1), AspNetPager1.PageSize, "myds");
        GridView1.DataSource = myds.Tables["myds"];        GridView1.DataKeyNames = new string[] { "id" };
        //主键
        GridView1.DataBind(); 
        sqlcon.Close();    }}