Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index'

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C#3.5

in the first page five records will be displayed and in the second page another five records will be displayed.

suppose in the first page i check two rows and in the second page i check another two rows means that selected check box rows to be update in the [transact].[transaction_item] in the table.

when i run below code shows error as follows

Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index.

The error shows in below line as follows

index = (int)grdRpt.DataKeys[gvrow.RowIndex].Value;

how to solve this error. please let me know.

What I have tried:

protected void Page_Load(object sender, EventArgs e)
        {
           if (!IsPostBack)
                {
                     BindData();
                }
       }


 protected void BindData()
        {
             String strConnString = ConfigurationManager.ConnectionStrings["ConnectionStrings"].ConnectionString;
                SqlConnection con = new SqlConnection(strConnString);
                SqlCommand cmd = new SqlCommand("select * from [transact].[transaction_item] where status = 'new'", con);
                con.Open();
                SqlDataAdapter da = new SqlDataAdapter();
                DataSet ds = new DataSet();
                da.SelectCommand = cmd;
                da.Fill(ds);
                grdRpt.DataSource = ds;
                grdRpt.DataBind();
        }


 protected void grdRpt_PageIndexChanging(object sender, GridViewPageEventArgs e)
        {
            grdRpt.PageIndex = e.NewPageIndex;
            BindData();
        }


private void PopulateCheckedValues()
        {
            System.Collections.ArrayList userdetails = (System.Collections.ArrayList)Session["CHECKED_ITEMS"];
            if (userdetails != null && userdetails.Count > 0)
            {
                foreach (GridViewRow gvrow in grdRpt.Rows)
                {
                    int index = (int)grdRpt.DataKeys[gvrow.RowIndex].Value;
                    if (userdetails.Contains(index))
                    {
                        CheckBox myCheckBox = (CheckBox)gvrow.FindControl("chkselecdata");
                        myCheckBox.Checked = true;
                    }
                }
            }
        }

   private void SaveCheckedValues()
        {
            System.Collections.ArrayList userdetails = new System.Collections.ArrayList();
            int index = -1;
            foreach (GridViewRow gvrow in grdRpt.Rows)
            {
                index = (int)grdRpt.DataKeys[gvrow.RowIndex].Value;
                bool result = ((CheckBox)gvrow.FindControl("chkselecdata")).Checked;

               
                if (Session["CHECKED_ITEMS"] != null)
                    userdetails = (System.Collections.ArrayList)Session["CHECKED_ITEMS"];
                if (result)
                {
                    if (!userdetails.Contains(index))
                        userdetails.Add(index);
                }
                else
                    userdetails.Remove(index);
            }
            if (userdetails != null && userdetails.Count > 0)
                Session["CHECKED_ITEMS"] = userdetails;
        }


 protected void btnsubmit_Click(object sender, EventArgs e)
        {
           String strConnString = ConfigurationManager.ConnectionStrings["ConnectionStrings"].ConnectionString;
                SqlConnection con = new SqlConnection(strConnString);
                con.Open();
                foreach (GridViewRow row in grdRpt.Rows)
                {
                    int key = (int)grdRpt.DataKeys[row.RowIndex].Value;
                    CheckBox cb = (CheckBox)row.FindControl("chkselecdata");
                    SqlCommand cmd = new SqlCommand("UPDATE [transact].[transaction_item] SET Status = 'Ready' Where Id=" + key.ToString(), con);
                    cmd.ExecuteNonQuery();
                }
                con.Close();
        }