error on paging

using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using Microsoft.SharePoint;
using System.Collections.Generic;
using System.Data;
namespace OperationProjectList.ProjectList
{
    public partial class ProjectListUserControl : UserControl
    {
        class Data
        {
            public string JobNO { get; set; }
            public string ProjectNo { get; set; }
            public string Delivery { get; set; }
        }
        protected void Page_Load(object sender, EventArgs e)
        {
            try
            {
                    DataTable data = Bindtogrid();
                    GridView1.DataSource = data;
                    GridView1.DataBind();
            }
            catch (Exception ex)
            {
            }
        }
        public DataTable Bindtogrid()
        {
            DataSet T = new DataSet();
            Data d = new Data();
            SPList projectlist = SPContext.Current.Web.Lists["ProLis"];
            List<Data> data = new List<Data>();
            DataTable dt = new DataTable();
            DataRow dr;
            dt.Columns.Add("JobNo");
            dt.Columns.Add("ProjectNo");
            dt.Columns.Add("Delivery");
            foreach (SPListItem item in projectlist.Items)
            {
                    //d.JobNO = item["JobNo"].ToString();
                    //d.ProjectNo = item["ProjectNo"].ToString();
                    //d.Delivery = item["Delivery"].ToString();
                    //data.Add(d);
                    dr = dt.Rows.Add();
                    dr["JobNo"] = item["JobNo"] + "";
                    dr["ProjectNo"] = item["ProjectNo"] + "";
                    dr["Delivery"] = item["Delivery"] + "";
            }
            return dt;
        }
      protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
        {
            GridView1.PageIndex = e.NewPageIndex;
            Bindtogrid();
        }
    }
}