System.InvalidCastException: 'Specified cast is not valid

Question

I want to make a system where i can show data from two table with two combobox but when i am about to complete i have shown this exception and i cann't solve this so please help me here is my full code..

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using Oracle.DataAccess.Client;
namespace combobox
{
public partial class Form1 : Form
{
List movies = new List();
List catagories = new List();
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
string connection = "Data Source = (DESCRIPTION = " +
"(ADDRESS = (PROTOCOL = TCP)(HOST = Mihadul)(PORT = 1521))" +
"(CONNECT_DATA =" +
"(SERVER = DEDICATED)" +
"(SERVICE_NAME = tick)" +
")" +
");User ID=mihadul;Password=mihadul123;";
OracleConnection con = new OracleConnection(connection);
con.Open();
OracleCommand cmdcat = new OracleCommand("SELECT * FROM CATOGORY", con);
OracleDataReader dr = cmdcat.ExecuteReader();
while (dr.Read())
{
cmb_catlist.Items.Add(dr["CAT_NAME"]);
catagories.Add(new Category()
{
cat_id = ((int)dr["cat_id"]),
cat_name = dr["cat_name"] as string
});
}
con.Close();
con.Open();
OracleCommand cmdmovie = new OracleCommand("SELECT * FROM MOVIES", con);
OracleDataReader dr1 = cmdmovie.ExecuteReader();
while (dr1.Read())
{
movies.Add(new Movie()
{
id = ((int)dr1["id"]),
movie_name = dr1["movie_name"] as string,
cat_id = ((int)dr1["cat_id"])
});
}
con.Close();
}
private string[] GetMovieById(int id)
{
return movies.Where(line => line.cat_id == id).Select(l => l.movie_name).ToArray();
}
private void cmb_catlist_SelectedIndexChanged(object sender, EventArgs e)
{
cmb_movlist.Items.Clear();
int id = catagories[cmb_catlist.SelectedIndex].cat_id;
foreach (string name in GetMovieById(id))
{
this.cmb_movlist.Items.Add(name);
}
}
}
[Serializable]
class Category
{
public int cat_id { get; set; }
public string cat_name { get; set; }
}
[Serializable]
class Movie
{
public int id { get; set; }
public string movie_name { get; set; }
public int cat_id { get; set; }
}
}