File copy in third folder after calculationg diff between first two folders

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C#

can anyone give the solution of following error in Application Code Part

startIndex cannot be larger than length of string.<br />
Parameter name: startIndex<br />

Code Part-//It's a files moving application...

protected static void copyDirectory(string Src, string Dst)
      {
          string targetPath = Dst.Substring(0, Dst.LastIndexOf(@"\") + 1);
          if (!System.IO.Directory.Exists(targetPath))
          {
              System.IO.Directory.CreateDirectory(targetPath);
          }
          File.Copy(Src, Dst, true);
      }

static FileInfo[] ListDirectory(string path)
       {
           return (new DirectoryInfo(path)).GetFiles("*.*", System.IO.SearchOption.AllDirectories);
       }

private void button1_Browse(object sender, EventArgs e)
       {
           DialogResult result = folderBrowserDialog1.ShowDialog();

           if (result == DialogResult.OK) // Test result.
           {
               textBox1.Text = folderBrowserDialog1.SelectedPath;

           }
}

try
{


FileInfo[] fileList1 = ListDirectory(dir1);
FileInfo[] fileList2 = ListDirectory(dir2);

var files1 = (from f1 in fileList1 select f1.FullName);

var filediff = (from f1 in files1 select f1.Substring(dir1.Length)).Intersect(from f2 in files2 select f2.Substring(dir1.Length));
foreach (String s in filediff)
{
copyDirectory(dir2 + s, name2 + s);
}

catch (IOException ex)
                       {
                           errlbl.Text = "*" + ex.ToString();
                       }
                   }

I've already taken the help of breakpoint but I am unable to solve it now I undwerlined it. plz resolve th error