ASP.NET

No overload for method 'Open' takes '1' arguments

xlBook = xlBooks.Item[1];

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            DataTable dt = (DataTable)Session["cart"];
            DataList1.DataSource = dt;
            DataList1.DataBind();
        }
    }
    protected void Datalist1_Update(object source, DataListCommandEventArgs e)
    {
        int ProductID = Convert.ToInt32(DataList1.DataKeys[e.Item.ItemIndex]);
        TextBox txtProductQty;
        txtProductQty = (TextBox)e.Item.FindControl("txtProductQty");
        string connectionstring = ConfigurationManager.ConnectionStrings["SilverOnline"].ConnectionString;
        SqlConnection conn = new SqlConnection(connectionstring);
        string str="Update Home Set ProductQty=@ProductQty Where(ProductID=@Productid)";
        SqlCommand cmd = new SqlCommand(str,conn);
        cmd.Parameters.Add("@ProductQty", SqlDbType.VarChar).Value = txtProductQty.Text; ;
        cmd.Parameters.Add("@Productid", SqlDbType.Int).Value = ProductID;
        if (conn.State == ConnectionState.Closed)
            conn.Open();
        cmd.ExecuteNonQuery();
        if (conn.State == ConnectionState.Open)
            conn.Close();
        DataList1.EditItemIndex = -1;
        DataTable dt = (DataTable)Session["cart"];
        DataList1.DataSource = dt;
        DataList1.DataBind();
    }