use.. to avoid back button
protected override void OnPreRender(EventArgs e)
{
base.OnPreRender(e);
string strDisAbleBackButton;
strDisAbleBackButton = "<script language='javascript'>\n";
strDisAbleBackButton += "window.history.forward(1);\n";
strDisAbleBackButton += "\n</script>";
ClientScript.RegisterClientScriptBlock(this.Page.GetType(), "clientScript", strDisAbleBackButton);
}