Постоянный InvalidOperationException при попытке установить datasource для грида

        string connstring = @"Data Source=ADMIN-PC\MSSQLSERVER2;
                              Initial Catalog=ShoppingMall;
                              Integrated Security=True";

string connection_string; //connection string
RadGridView rgv; //temporary grid view
SqlCommand cmd; //any command
private Thread DBConnectionThread; //thread for connection
public event EventHandler ConnectionComplete; //event for connection
SqlDataReader reader; //execute reader
string cmd_text; //query

md_text = "Select * from TServiceContract";
 
this.radWaitingBarElement1.Visibility = ElementVisibility.Visible;
this.radWaitingBarElement1.StartWaiting();
 
this.Connect();
this.ConnectionComplete += db_ConnectionComplete;
 
this.radLabelElement1.Text = "Connection to database established!";

public void Connect()
        {
            DBConnectionThread = new Thread(new ThreadStart(this.EstablishConnection));
            DBConnectionThread.Start();
        }

private void EstablishConnection()
        {
            using (SqlConnection conn = new SqlConnection(connection_string))
            {
                using (cmd = conn.CreateCommand())
                {
                    cmd.CommandText = cmd_text;
                    try
                    {
                        Thread.Sleep(5000);//temporary waiting
                        conn.Open();
                    }
                    catch (Exception) { }
 
                    if (this.ConnectionComplete.Target is System.Windows.Forms.Control)
                    {
                        System.Windows.Forms.Control target = ConnectionComplete.Target as System.Windows.Forms.Control;
                        target.BeginInvoke(this.ConnectionComplete, new Object[] { });
                    }
                    else
                    {
                        this.ConnectionComplete(this, EventArgs.Empty);
                    }
 
                    reader = cmd.ExecuteReader();
                }
            }
        }

private void db_ConnectionComplete(object sender, EventArgs e)
        {
 
            rgv = new RadGridView();
            rgv.Size = new Size(753, 427);
            rgv.Location = new Point(0, 54);
            rgv.AutoGenerateColumns = true;
            rgv.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
            rgv.DataSource = reader; //InvalidOperationException(HasRows,FieldCount,Depth threw this exception)
            this.Controls.Add(rgv);
 
            this.radLabelElement1.Text = "Data was loaded from database";
            this.radWaitingBarElement1.Visibility = ElementVisibility.Hidden;
        }