C# 连接Oracle数据库提示未将对象引用到实例

调试时出现“ServerVersion = 'conn.ServerVersion' threw an exception of type 'System.InvalidOperationException'”的错误源代码如下：
using System;
using System.Collections.Generic;
//using System.Data.OracleClient;
using System.Linq;
using System.Text;
using Oracle.DataAccess.Client;
using System.Windows.Forms;namespace Text.Connect.Demo
{
    class Program
    {
        static void Main(string[] args)
        {
            OracleConnection conn = new OracleConnection();
            string connString = "Data Source=(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=117.29.161.242)(PORT=1521))(CONNECT_DATA=(SERVER = DEDICATED)(SERVICE_NAME = GJCARREVEN)));User Id=joysv2;Password=joysv2";
            conn = new OracleConnection(connString);
            if (conn != null)
            {
                MessageBox.Show(conn.ToString());
                MessageBox.Show(connString);
            }
            try
            {               
                conn.Open();
                MessageBox.Show(conn.State.ToString());
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message.ToString());
            }
            finally
            {
                conn.Close();
            }
        }
    }
}