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    private bool readBlockFromFile(SecureString fileName, ref byte[] b, long pos)
    {
      IntPtr p = System.Runtime.InteropServices.Marshal.SecureStringToBSTR(fileName);

      try
      {
         using (System.IO.MemoryMappedFiles.MemoryMappedFile objMF = 
             System.IO.MemoryMappedFiles.MemoryMappedFile.CreateFromFile(
           System.Runtime.InteropServices.Marshal.PtrToStringUni(p),
             System.IO.FileMode.Open, "NewTextFile" ))
       
             using (System.IO.MemoryMappedFiles.MemoryMappedViewAccessor accessor = 
                 objMF.CreateViewAccessor(100, 100))
             {  
                 accessor.ReadArray(pos, b, 0, b.Length);
             }
       
        return true;
      }
      catch {MessageBox.Show("Fehler");return false;}
      finally  {Marshal.ZeroFreeBSTR(p);}  
    }