ATL /RichEdit

HI,
I created a dumyy dialog project in vc++ and added ATL support to it. The process of adding ATL changes the stdafx.h and the main application (.h and .cpp). One of the method that gets added is InitAtl ().

Part of the code in InitATL ():
#if _WIN32_WINNT >= 0x0400
HRESULT hRes = CoInitializeEx(NULL, COINIT_MULTITHREADED);
#else
HRESULT hRes = CoInitialize(NULL);
#endif

In need to use CoInitializeEx in my project, so defined the _WIN32_WINNT in my stdafx.h

Now the app does not come up at all. If i comment out the #define for _WIN32_WINNT, it works OK. The dialog project has a CRichEditCtrl on the main dialog.
Thanks in advance..