May be you have included
"CDragDrop.h" file before
"stdafx.h", as follow:
#include "CDragDrop.h"
#include "stdafx.h"
to fix the problem, write all the file inclusions after the
#include "stdafx.h"
statement.
It should be like this:
#include "stdafx.h"
#include "CDragDrop.h"