dropdownlist error in c# code

i want to show a value in DropDownList at page load and the value is "1 Year". here is my Database Table

id  instal
0   Choose
6   6 Month
12  1 Year
24  2 Year
36  3 Year

here is my ASPX code:

<%@ Page Title="" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true" CodeFile="Default3.aspx.cs" Inherits="Default3" %>

<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" Runat="Server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" Runat="Server">
    <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" 
        DataSourceID="SqlDataSource1" DataTextField="instal" DataValueField="id" 
        onselectedindexchanged="DropDownList1_SelectedIndexChanged">
    </asp:DropDownList>
    <asp:SqlDataSource ID="SqlDataSource1" runat="server" 
        ConnectionString="<%$ ConnectionStrings:paconn %>" 
        SelectCommand="SELECT * FROM [cms_instal] ORDER BY [id]">
    </asp:SqlDataSource>
</asp:Content>

and its my C# code:

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.Sql;
using System.Data.SqlClient;
using System.Collections;
using System.Web.SessionState;

public partial class Default3 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        DropDownList1.Text = "1 Year";
    }
    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {

    }
}

but problem is that when my page is loaded it gives an error "'DropDownList1' has a SelectedValue which is invalid because it does not exist in the list of items. Parameter name: value"

i am using ASP.Net C#, SQL Server 2008.