Error @ runtime in table to xml doc conversion.

protected void Button1_Click(object sender, EventArgs e)

{

 string connString = @"server = .\sqlexpress;integrated security = true;database = northwind";

 string qry = @"select productname,unitprice from products";

 SqlConnection conn = new SqlConnection(connString);

 try

 {

     SqlDataAdapter da = new SqlDataAdapter();

     da.SelectCommand = new SqlCommand(qry, conn);

     conn.Open();

     DataSet ds = new DataSet();

     da.Fill(ds, "products");

     Console.WriteLine("Creating");

     ds.WriteXml(@"c:\productstable.xml");

     Console.WriteLine("Done");

 }

 catch (Exception e1)

 {

     Console.WriteLine("Error: " + e1);

 }

 finally

 {

     conn.Close();

 }

 }

Error!

The thread 0xba4 has exited with code 0 (0x0).

A first chance exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll