What might be causing this ?

I've got this code:

Code:

#include "stdafx.h"
#include <bitset>

void someFunction(std::string str){
     std::bitset<8> firstChar[str[0]);
}

Everything compiles correctly here. When I change order of includes it won't compile any more. What could possibly cause it ?

Code:

#include <bitset>
#include "stdafx.h"

void someFunction(std::string str){
      std::bitset<8> firstChar[str[0]);
}

error C2039: 'bitset' : is not a member of 'std'

That's a problem with using precompiled headers in a project I think(?). The "stdafx.h" one must always come first I believe. It's one reason I don't like using them in my projects, order of header includes should not affect compilation.