I have a CDialog , i decleared the Combobox in .rc file , i can see that combobox on screen but as soon as i do DDX mapping of this combobox , dialog dont open and produces asseetion failed. I have added other combobox in same dialog but addidtion of this combobox produces above mentioned problem.Sample code are below:

Code:
// Mydialog.h
CComboBox  combo_one ;
CComboBox  combo_two;
CComboBox  combo_three;
CComboBox  combo_four;
//MyDialog.cpp
Code:
void MyDialog :: DoDataExchange(CDataExchange* pDX)
{
DDX_Control(pDX, IDC_COMBO_ONE, combo_one);
DDX_Control(pDX, IDC_COMBO_TWO, combo_two);
DDX_Control(pDX, IDC_COMBO_THREE, combo_three);
DDX_Control(pDX, IDC_COMBO_FOUR, combo_four);
}
//Mydialog.rc
Code:
COMBOBOX   IDC_COMBO_ONE, 10.,20,30,40, CBS_DROPDOWN
COMBOBOX   IDC_COMBO_TWO, 20.,30,30,40, CBS_DROPDOWN
COMBOBOX   IDC_COMBO_THREE, 30.,40,30,40, CBS_DROPDOWN
COMBOBOX   IDC_COMBO_FOUR,40,50,30,40, CBS_DROPDOWN
i am getting no error when i added and mapped IDC_COMBO_ONE, IDC_COMBO_TWO,IDC_COMBO_THREE but as soon as i mapped IDC_COMBO_FOUR in DoDataExchange , error of assertion failed comes.
I debugged and found that when i hover combo_four variable during debug its hwnd is null while other three varaible have some memory.