enum versus private enum

[shawnlau]

The following code works in VC++ 2010 but generates numerous errors in VC++ 2012:

#include "stdafx.h"

using namespace System;

enum class Months{January = 1, February, March, April };

int main(array<System::String ^> ^args)
{
Months month;
int value;

month = Months::January;
value = safe_cast<int>(month);
Console::WriteLine(L"Month is {0} and the value is {1}.", month, value);



return 0;
}

In order to compile in VC++ 2012, the code must be changed to:

private enum class Months{January = 1, February, March, April };

My question is why?
Is VC++ so chaotic that code from one version won't compile in another version? Doesn't that defy the idea of portable code?