請問一下為什麼這樣寫執行到openread那一行後都會顯示權限不足呢？
我上網翻了許久都翻不到，請求大神幫助，感謝您。

using System;
using Renci.SshNet;
using Renci.SshNet.Sftp;
using System.IO;
using System.Linq;
using System.Text;
using System.Collections.Generic;
using System.Xml;


//連接SFTP之功能
namespace ConsoleApp1
{
    class Program 
    {
        private static string _host = "";
        private static string _username = "";
        private static string _password = "";
        static void Main(string[] args)
        {
            
            var sftp = new SftpClient(_host, _username, _password);
            try
            {
                sftp.Connect();
                if (sftp != null)
                {
                    string a = collectDoc(sftp);
                    if (a != "f")
                    {
                        var doc = new XmlDocument();
                        doc.Load(sftp.OpenRead(a));
                        PackDocument pD = new PackDocument(a,doc);
                    }
                    else
                    {
                        
                    }
                    
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e);
            }
            finally
            {
                if (sftp != null || sftp.IsConnected)
                {
                    sftp.Disconnect();
                }
            }
        }

       
        //取得所有檔案
        private static string collectDoc(SftpClient sftp) 
        {
            string errorMessage = "";
            List<string> fileList = new List<string>();
            //using(sftp)
            //{
                Action<SftpFile> ShowDirOrFile = (item) =>
                {
                    if (item.IsDirectory)
                    {
                        Console.WriteLine($"[{item.Name}]");
                    }
                    else
                    {
                        Console.WriteLine($"[{item.Name:-32}{item.Length,8:N0}]");
                    }
                };

                Action<string> Dir = (path) =>
                {
                    Console.ForegroundColor = ConsoleColor.Yellow;
                    Console.WriteLine($"Directory of {path}: \n");
                    var list = sftp.ListDirectory(path).Where(o => !".,..".Split(',').Contains(o.Name)).ToList();
                    if (list.Any())
                    {
                        list.ForEach(ShowDirOrFile);
                    }
                    else
                    {
                        Console.ForegroundColor = ConsoleColor.DarkYellow;
                        Console.WriteLine("NO files.");
                    }
                    Console.WriteLine();
                    Console.ForegroundColor = ConsoleColor.White;
                };
                Dir("/");                
                var listDirectory = sftp.ListDirectory("/");
                try
                {
                    foreach (var i in listDirectory)
                    {
                        string xmlName = i.Name;
                        return xmlName;
                    }
                }
                catch (Exception e)
                {
                    Console.WriteLine(e);
                    return "f";
                }
                return "f";
            //}      
        }
    }
}