error on changing the index when pageindex or selected rowindex in grid view

Question

Hi

IN My application i am using  grid, and binging the grid with list, and in the i applying 2 events selected index changed and pageindex changing event when i am clicking on a footer page index it is working and when i am trying to click on the second time it causes the following error and if try to select a record by clicking on select button also it causes the same error

please check this error and post the comments or mistakes in it

if you want the code

<asp:Content ID="Content3" ContentPlaceHolderID="cphContent" runat="server">
    <asp:GridView ID="gvInvoiceslist"  AutoGenerateColumns="false"
        runat="server" OnSelectedIndexChanged="ViewInvoiceByRefId"
        AllowPaging="true" onpageindexchanging="gvInvoiceslist_PageIndexChanging">
        <Columns>
        <asp:CommandField ButtonType="Image" EditText="View" ShowEditButton="true"/>
        <asp:TemplateField>       
        <ItemTemplate>
        <asp:HiddenField id="hdnrefid" Value='<%#Eval("InvoiceRefID") %>' runat="server" />
        </ItemTemplate>       
        </asp:TemplateField>
        <asp:BoundField HeaderText="ClientName" DataField="ClientName" />
        <asp:BoundField HeaderText="InvoiceNumber" DataField="InvoiceNumber" />
        <asp:BoundField HeaderText="Preparername" DataField="Preparername" />
        <asp:BoundField HeaderText="TotalFees" DataField="TotalFees" />
        <asp:BoundField HeaderText="TotalAmount" DataField="TotalAmount" />   
        </Columns>
        </asp:GridView>
</asp:Content>

.aspx.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using LOSIMSystem.BLL.Controllers;
namespace LOSIMSystem.Admin
{
    public partial class InvoiceArchieved : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            BindInvoicesToGrid();
        }
        private void BindInvoicesToGrid()
        {
            InvoiceController invctrl = new InvoiceController();
            gvInvoiceslist.DataSource = invctrl.GetAllInvoices();
            gvInvoiceslist.DataBind();
        }

       
        protected void ViewInvoiceByRefId(object sender, EventArgs e)
        {
            int srowindex = gvInvoiceslist.SelectedIndex;

            int refid =Convert.ToInt16(((HiddenField)gvInvoiceslist.Rows[srowindex].FindControl("hdnrefid")).Value);

            InvoiceController invoicectrl = new InvoiceController();
            Common.BussinessObjects.BLInvoice blinvoice= invoicectrl.GetInvoice(refid);

            Response.Redirect("viewinvoice.aspx?hiddenid=" + refid);
        }

        protected void gvInvoiceslist_PageIndexChanging(object sender, GridViewPageEventArgs e)
        {
            gvInvoiceslist.PageIndex = e.NewPageIndex;
        }


      
      
    }
}