Problem with event of DataList

<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
    <%--<table>
        <tr>

            <td style="padding-left: 9px;">
                <br />
                layoutId :
                <asp:Label ID="Label1" runat="server" Text=""></asp:Label>
                <br />
                storeID :<asp:Label ID="Label2" runat="server" Text=""></asp:Label>
                <br />
                store_name :<asp:Label ID="Label3" runat="server" Text=""></asp:Label>
                <br />
                site_name :<asp:Label ID="Label4" runat="server" Text=""></asp:Label>
                <br />
                stores_status :<asp:Label ID="Label5" runat="server" Text=""></asp:Label>
                <br />
                UserID :<asp:Label ID="Label6" runat="server" Text=""></asp:Label>
                <br />
                HigherAccess :<asp:Label ID="Label7" runat="server" Text=""></asp:Label>
                <br />
                AccessLevel :<asp:Label ID="Label8" runat="server" Text=""></asp:Label>
                <br />
                SubFolderName :<asp:Label ID="Label9" runat="server" Text=""></asp:Label>
            </td>
        </tr>
    </table>--%>
    <table border="0" cellspacing="0" cellpadding="0" width="100%">
        <tr>
            <td>
            <br />
            <br />
            <br />
            <br />
                <asp:DataList ID="dlProductList" runat="server" RepeatColumns="4" RepeatDirection="Horizontal"
                    Height="235px" Width="788px">
                    <ItemTemplate>
                        <table>
                            <tr>
                                <td>
                                    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<asp:Image ID="imgProductImage" runat="server"
                                       ImageUrl='<%#GetImage(Convert.ToString(DataBinder.Eval(Container.DataItem,"imagename")))%>' />
                                    <br />
                                    <asp:LinkButton ID="lbProductName" runat="server" Text='<%#Bind("name")%>'> </asp:LinkButton>
                                </td>
                            </tr>
                        </table>
                    </ItemTemplate>
                </asp:DataList>
            </td>
        </tr>
    </table>
    <table>
        <tr>
            <td>
                <asp:LinkButton ID="lbtnFirst" runat="server" CausesValidation="false" OnClick="lbtnFirst_Click">First</asp:LinkButton>
           </td>
           <td>
                <asp:LinkButton ID="lbtnPrev" runat="server" CausesValidation="false" OnClick="lbtnPrevious_Click">Previous</asp:LinkButton>
            </td>
            <td>
                <asp:DataList ID="dlPaging" runat="server" RepeatDirection="Horizontal" OnItemCommand="dlPaging_ItemCommand"
                    OnItemDataBound="dlPaging_ItemDataBound">
                    <ItemTemplate>
                        <asp:LinkButton ID="lnkbtnPaging" runat="server" CommandArgument='<%# Bind("PageIndex") %>'
                            CommandName="Paging" Text='<%#Bind("PageText")%>'></asp:LinkButton>
                    </ItemTemplate>
                </asp:DataList>
            </td>
            <td>
                <asp:LinkButton ID="lbtnNext" runat="server" CausesValidation="false" OnClick="lbtnNext_Click">Next</asp:LinkButton>
            </td>
            <td>
                <asp:LinkButton ID="lbtnLast" runat="server" CausesValidation="false" OnClick="lbtnLast_Click">Last</asp:LinkButton>
           </td>
        </tr>
    </table>
</asp:Content>

if (!Page.IsPostBack)
             {
                 this.SelectProductDetails();
             }
        }
        
        private int CurrentPage
        {
            get
            {
                object objPage = ViewState["_CurrentPage"];
                int _CurrentPage = 0;
                if (objPage == null)
                {
                    _CurrentPage = 0;
                }
                else
                {
                    _CurrentPage = (int)objPage;
                }
                return _CurrentPage;
            }
            set { ViewState["_CurrentPage"] = value; }
        }
        private int firstIndex
        {
            get
            {
                int _FirstIndex = 0;
                if (ViewState["_FirstIndex"] == null)
                {
                    _FirstIndex = 0;
                }
                else
                {
                    _FirstIndex = Convert.ToInt32(ViewState["_FirstIndex"]);
                }
                return _FirstIndex;
            }
            set { ViewState["_FirstIndex"] = value; }
        }
        private int lastIndex
        {
            get
            {
                int _LastIndex = 0;
                if (ViewState["_LastIndex"] == null)
                {
                    _LastIndex = 0;
                }
                else
                {
                    _LastIndex = Convert.ToInt32(ViewState["_LastIndex"]);
                }
                return _LastIndex;
            }
            set { ViewState["_LastIndex"] = value; }
        }
       
        private void SelectProductDetails()
        {
            BAL.BalDepartment ObjDepartment = new BAL.BalDepartment();
           // DataTable dt = ObjDepartment.SelectProductDetails(Convert.ToInt32(Session["storeID"]));
            DataTable dt = ObjDepartment.SelectProductDetails(318);
            if (dt != null && dt.Rows.Count > 0)
            {
                _PageDataSource.DataSource = dt.DefaultView;
                _PageDataSource.AllowPaging = true;
                _PageDataSource.PageSize = 12;
                _PageDataSource.CurrentPageIndex = CurrentPage;
                ViewState["TotalPages"] = _PageDataSource.PageCount;
                this.dlProductList.DataSource = _PageDataSource;
                this.dlProductList.DataBind();
                this.doPaging();
                //dlProductList.DataSource = dt;
                //dlProductList.DataBind();
            }
     
        }
        private void doPaging()
        {
            DataTable dt = new DataTable();
            dt.Columns.Add("PageIndex");
            dt.Columns.Add("PageText");
            firstIndex = CurrentPage - 5;
            if (CurrentPage > 5)
            {
                lastIndex = CurrentPage + 5;
            }
            else
            {
                lastIndex = 12;
            }
            if (lastIndex > Convert.ToInt32(ViewState["TotalPages"]))
            {
                lastIndex = Convert.ToInt32(ViewState["TotalPages"]);
                firstIndex = lastIndex - 12;
            }
            if (firstIndex < 0)
            {
                firstIndex = 0;
            }
            for (int i = firstIndex; i < lastIndex; i++)
            {
                DataRow dr = dt.NewRow();
                dr[0] = i;
                dr[1] = i + 1;
                dt.Rows.Add(dr);
            }
            this.dlPaging.DataSource = dt;
            this.dlPaging.DataBind();
        }
        protected void dlPaging_ItemCommand(object source, DataListCommandEventArgs e)
        {
            if (e.CommandName.Equals("Paging"))
            {
                CurrentPage = Convert.ToInt16(e.CommandArgument.ToString());
                this.SelectProductDetails();
            }
        }
        protected void dlPaging_ItemDataBound(object sender, DataListItemEventArgs e)
        {
            LinkButton lnkbtnPage = (LinkButton)e.Item.FindControl("lnkbtnPaging");
            if (lnkbtnPage.CommandArgument.ToString() == CurrentPage.ToString())
            {
                lnkbtnPage.Enabled = false;
                lnkbtnPage.Style.Add("fone-size", "14px");
                lnkbtnPage.Font.Bold = true;
            }
           // dlPaging.ItemCommand += new DataListCommandEventHandler(this.dlPaging_ItemCommand);
        }
        protected void lbtnFirst_Click(object sender, EventArgs e)
        {
            CurrentPage = 0;
            this.SelectProductDetails();
        }
        protected void lbtnPrevious_Click(object sender, EventArgs e)
        {
            if (CurrentPage != 0)
            {
                CurrentPage -= 1;
                this.SelectProductDetails();
            }
            else
            {
                CurrentPage = 0;
                this.SelectProductDetails();
            }
        }
        protected void lbtnNext_Click(object sender, EventArgs e)
        {
            int val=Convert.ToInt32(ViewState["TotalPages"]);
            int cunval = CurrentPage;
            if (CurrentPage < val-1)
            {
                CurrentPage += 1;
                this.SelectProductDetails();
            }
            else
            {
                CurrentPage = val-1;
                this.SelectProductDetails();
            }
        }
        protected void lbtnLast_Click(object sender, EventArgs e)
        {
            CurrentPage = (Convert.ToInt32(ViewState["TotalPages"]) - 1);
            this.SelectProductDetails();
        }
        
        public string GetImage(string Imagename)
        {
          if(Imagename!=null)
            return SavePath + Imagename;
          else 
            return SavePath+"NoImage.jpg";
          
        }