Classe Csharp Erro no metodo update utilizando a classe conexaosql

  string k =Request.QueryString["id_corrida"];
        SqlConnection cnn = new SqlConnection(@"Data Source=_______________;Initial Catalog=db_site;Persist Security Info=True;User ID=site_lab;Password=203010..");
        cnn.Open();
        SqlCommand cmd = cnn.CreateCommand();
        cmd.Parameters.Add(new SqlParameter("@PARAMETRO", drpMotoTrabalhando.SelectedValue.ToString()));
        cmd.Parameters.Add(new SqlParameter("@ID_CORRIDA", k.ToString()));
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "UPDATE tb_corridas SET nr_motoqueiro = @PARAMETRO WHERE id_corrida = @ID_CORRIDA";
             cmd.ExecuteNonQuery();
        cnn.Close();

 //#########TESTAR SOMENTE NO BANCO DE BACKUPS 


        string k =Request.QueryString["id_corrida"];
        conexao_sql_server cnn = new conexao_sql_server();
        cnn.Open();
        SqlCommand cmd = cnn.CreateCommand();
        SqlCommand cmd = new SqlCommand();
        cmd.Parameters.Add(new SqlParameter("@PARAMETRO", drpMotoTrabalhando.SelectedValue.ToString()));
        cmd.Parameters.Add(new SqlParameter("@ID_CORRIDA", k.ToString()));
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "UPDATE tb_corridas SET nr_motoqueiro = @PARAMETRO WHERE id_corrida = @ID_CORRIDA";
        
        cmd.ExecuteNonQuery();
        cnn.Close();
        Response.Redirect("~/atendentes/corridas.aspx");

    private const string _strCon = @"Data Source=192.xxx.zzz.kkk;Initial Catalog=db_site;Persist Security Info=True;User ID=site_lab;Password=302010..";
    private string vSql = "";



    public string VSql
    {
        get { return vSql; }
        set { vSql = value; }
    }
    private SqlConnection objCon = null;

    public SqlConnection ObjCon
    {
        get { return objCon; }
        set { objCon = value; }
    }




    public bool Conectar()
    {
        ObjCon = new SqlConnection(_strCon);
        try
        {
            ObjCon.Open();
            return true;
        }

        catch
        {
            return false;

        }



    }

    public bool DesConectar()
    {

        if (ObjCon.State != ConnectionState.Closed)
        {
            ObjCon.Close();
            ObjCon.Dispose();
            return true;

        }
        else
        {
            ObjCon.Dispose();
            return false;

        }
    }


    public bool verificaConexao()
    {

        if (ObjCon.State == ConnectionState.Open)
        {
            ObjCon.Close();
            ObjCon.Dispose();
            return true;

        }
        else
        {
            ObjCon.Dispose();
            return false;


        }
    }




    public conectaSql()
    {
        //
        // TODO: Add constructor logic here
      //
    }
}