'column' Argument Cannot Be Null.

Hi i get the above error whenever i try and run my page, what i am trying to do is embed a repeater within a datalist, here is my code;public void Page_Load(object sender, EventArgs e)

{string strID = Request.QueryString["id"];

SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["streamConnectionString"].ConnectionString);SqlCommand command = new SqlCommand("stream_Users", conn);

command.CommandType = CommandType.StoredProcedure;command.Parameters.Add("@userID", SqlDbType.Int).Value = Request.QueryString["id"];

SqlDataAdapter cmd1 = new SqlDataAdapter(command);

//Create and fill the DataSet.DataSet ds = new DataSet();

cmd1.Fill(ds, "userName");

//Create a second DataAdapter for the Titles table.SqlDataAdapter cmd2 = new SqlDataAdapter("select * from UserSpecialties", conn);

cmd2.Fill(ds, "specialty");

//Create the relation bewtween the Authors and Titles tables.ds.Relations.Add("myrelation",

ds.Tables["userName"].Columns["userID"],ds.Tables["specialtyName"].Columns["userID"]);

//Bind the Authors table to the parent Repeater control, and call DataBind.DataList1.DataSource = ds.Tables["userName"];

Page.DataBind();

//Close the connection.

conn.Close();

}