error in retrieving pc's content in c# in vs2008 in windows 7

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Security;
using System.Security.Permissions;

namespace ConsoleApplication2
{
    class Class1
    {
        StreamWriter sw = new StreamWriter("D:\\contents.txt");
        public void getfil(String path)
        {
            string[] p = Directory.GetFiles(path);
            for (int j = 0; j < p.Length; j++)
            {
                sw.WriteLine(p[j]);
                Console.WriteLine(p[j]);
            }
        }
        public void getfol(string path)
        {
            
            int i;
            try
            {
                string[] a = Directory.GetDirectories(path);
                for ( i = 0; ; i++)
                {
                
                    sw.WriteLine(a[i]);
                    Console.WriteLine(a[i]);
                   
                            bool isa = ((File.GetAttributes(a[i]) & FileAttributes.System) == FileAttributes.System);
                            if (isa == true)
                            {
                                sw.WriteLine("Idetifier");
                                Console.WriteLine("");

                                i++;

                            }
                           
                        if (Directory.GetDirectories(a[i]).Length > 0)
                        {
                            
                                getfol(a[i]);
                            

                        }


                        if (Directory.GetFiles(a[i]).Length > 0)
                        {
                                getfil(a[i]);
                            
                
                       }
                        
                }
                sw.Close();
                Console.WriteLine("Done");
            }
            
            catch (Exception e)
            
            {
              
            }
          
        }
    }
}