Allow paging property of Gridview gives a problem..in asp.net..

Because You Used Datareader which works in forward only manner.<br />
Use Dataset or Datatable[Dataadpter] which supports both forward and backward navigation.

protected void Page_Load(object sender, EventArgs e)
   {
       if (!Page.IsPostBack)
       {

           Binddata();


       }
   }
   public void Binddata()
   {

   string connect=System.Configuration.ConfigurationManager.ConnectionStrings["conn"].ConnectionString;
   SqlConnection sqlconn = new SqlConnection(connect);
   SqlDataAdapter da = new SqlDataAdapter("select * from persons",sqlconn);
   DataSet ds = new DataSet();
   da.Fill(ds);
   sqlconn.Open();

   GridView1.DataSource = ds.Tables[0];
   GridView1.DataBind();

   sqlconn.Close();



   }

protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
   {
       GridView1.PageIndex = e.NewPageIndex;
       Binddata();

   }