我在哪里做错了什么？执行时出错（运行时错误）

我做错了什么 我收到一个错误：在此行中：

Buffer.BlockCopy((Array) numArray, icondirentry.ImageOffset, (Array)
                 iconFile.iconImage[index], 0, icondirentry.BytesInRes);

错误：数组的偏移量和长度超出范围，或者计数大于从索引到源集合末尾的元素数。

此方法的完整代码为：

 public static IconClass.IconFile FromFile(string filename)
      {
        IconClass.IconFile iconFile = new IconClass.IconFile();
        byte[] numArray = File.ReadAllBytes(filename);
        GCHandle gcHandle = GCHandle.Alloc((object) numArray, GCHandleType.Pinned);
        iconFile.iconDir = (IconClass.ICONDIR) Marshal.PtrToStructure(gcHandle.AddrOfPinnedObject(), typeof (IconClass.ICONDIR));
        iconFile.iconEntry = new IconClass.ICONDIRENTRY[checked ((int) iconFile.iconDir.Count - 1 )];
        iconFile.iconImage = new byte[checked ((int) iconFile.iconDir.Count - 1)][];
        int num1 = Marshal.SizeOf((object) iconFile.iconDir);
        Type type = typeof (IconClass.ICONDIRENTRY);
        int num2 = Marshal.SizeOf(type);
        int num3 = 0;
        int num4 = checked ((int) iconFile.iconDir.Count - 1);
        int index = num3;
        while (index <= num4)
        {
          IconClass.ICONDIRENTRY icondirentry = (IconClass.ICONDIRENTRY) Marshal.PtrToStructure(new IntPtr(checked (gcHandle.AddrOfPinnedObject().ToInt64() + (long) num1)), type);
          iconFile.iconEntry[index] = icondirentry;
          iconFile.iconImage[index] = new byte[checked (icondirentry.BytesInRes - 1 )];
          Buffer.BlockCopy((Array) numArray, icondirentry.ImageOffset, (Array) iconFile.iconImage[index], 0, icondirentry.BytesInRes);
          checked { num1 += num2; }
          checked { ++index; }
        }
        gcHandle.Free();
        return iconFile;
      }