remove_if under visual c++.net 2005

Hi, all:

I write a vector contain complex objects, and use flag to identify
them, when flag=1, then use remove_if to delete the element, following
is a simplified form of that code which work well under g++ 3.4.3, but
under Visual C++.net 2005, it cannot be compiled, the message is
"...... error C3861: remove_if: cannot find identifier", can anybody
help?

///////////////////////////////////////////////////////////////
#include "stdafx.h" //Deleted under Linux
#include <vector>
#include <iostream>

struct A {
   int value;
   int flag;
   friend class IsFlag;
}a;

class IsFlag {
   public:
   bool operator() (const A &rhs) {
       return (rhs.flag ==1)?true:false;
    }
};

int main () {
   int i;
   std::vector <A> N;

   for (i=0; i<10; i++) {
      a.value = i;
      a.flag = 0;
      if (i%3 == 0) a.flag = 1;
      N.push_back(a);
   }

   N.erase(remove_if(N.begin(),N.end(),IsFlag()),N.end());

   return 1;
}

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