The following example works for me (you'll need to substitute a connection string). Is there a possibility that you are not getting back from your data access class the information you think you are?

<script runat="server">


    void Button1_Click(object sender, EventArgs e) {
       //DataSet ds = SqlHelper.ExecuteDataset(SPString, CommandType.StoredProcedure, "sp_name", parameters);
       DataSet ds = GetData();
       StringWriter tw = new StringWriter();
       HtmlTextWriter hw = new HtmlTextWriter(tw);
       dgdownload.DataSource = ds.Tables[0];
       dgdownload.DataBind();
       Response.ContentType = "application/vnd.ms-excel";
       Response.Charset = "";
       Page.EnableViewState = false;
       dgdownload.RenderControl(new HtmlTextWriter(tw));
       tw.Flush();
       tw.Close();
    }
    

    DataSet GetData() {
       // Substitute a connection string
       string connectionString = "server=MYSERVER; trusted_connection=true; database=DATABASE";
       SqlConnection dbConnection = new SqlConnection(connectionString);
    

       // Substitute a query
       string queryString = "SELECT GuestName, EntryDate, Comment FROM Guestbook";
       SqlCommand dbCommand = new SqlCommand(queryString, dbConnection);
    

       SqlDataAdapter dataAdapter = new SqlDataAdapter();
       dataAdapter.SelectCommand = dbCommand;
       DataSet dataSet = new DataSet();
       dataAdapter.Fill(dataSet);
       return dataSet;
    }


</script>




    <form runat="server">
        


            
        


        


            
        


    </form>