DropdownList DataBinding

[sonia sardana]

<connectionStrings>
    <add name="ConnectionString" connectionString="Data Source=(local);Initial catalog=sonia;User ID=sonia;Password=sonia;" providerName="System.Data.SqlClient"/>
  </connectionStrings>

public partial class Frmgrid : System.Web.UI.Page
{
    SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
    SqlDataAdapter da;
    DataSet ds;

    protected void Page_Load(object sender, EventArgs e)
    {
        try
        {
            da = new SqlDataAdapter("SELECT * FROM Products", conn);
            da.Fill(ds, "tb1");
            DropDownList1.DataSource = ds.Tables["tb1"];
            DropDownList1.DataBind();
        }
        catch (Exception ex)
        {
            Response.Write(ex.Message.ToString());
        }
    }        
}

ERROR is dere while executing the line da.Fill(ds, "tb1");
"Value cannot be null.\r\nParameter name: dataSet"

[guru_sarkar]

You must intialize ds
e.g. DataSet ds = new DataSet();

Check this eg:
http://msdn.microsoft.com/en-us/library/bh8kx08z(VS.80).aspx