Problem with checking Checkbox

So,I'm enumerating all the childs of a window,and using this as a processor:

LONG style;
	style = GetWindowLong(hwnd, GWL_STYLE);
	if((style & BS_TYPEMASK) == BS_AUTOCHECKBOX){
		MessageBox(NULL,"check","",NULL);
		PostMessage(hwnd, BM_SETCHECK, BST_CHECKED, 0);
	}
	return TRUE ;

I checked it,there is a checkbox with that style.Why doesn't it work?