Code for Logout

Hi Everyone,

Please help me in writing code for logout in asp.net..My webapplication is not having site.master page...

In my aspx page...

<a id="Logout" runat="server">Logout</a>

In aspx.cs page...

protected void Page_Load(object sender,EventArgs e)

{

Logout.ServerClick+=new EventHandler(btnLogout_Click);

}

protected void btnLogout_Click(object sender,EventArgs e)

{

try
{
Session.Abandon();

Response.Cache.SetCacheability(HttpCacheability.NoCache);
Response.Buffer = true;
Response.ExpiresAbsolute = DateTime.Now.AddDays(-1d);
Response.Expires = -1000;
Response.CacheControl = "no-cache";
Response.Redirect("index.aspx", true);
}
catch (Exception ex)
{
Response.Write(ex.Message);
}

}

I have used above code in all my aspx and aspx.cs pages...But i am not able to logout from page...

I am getting _doPostBack is undefined error....

Please send me other alternative...If i click back button also it should not show logged in pages...I have tried but not able to achieve my requirement...

Thanks in advance...