Debug assertion failed for CDialog::CreateEx

I am doing an MFC application in which I am trying to create a dialog box.

Here is my code snippet:

// GLobals:

CWnd* parent;

CRect rect3;

virtual BOOL OnInitDialog()
{

...

GetDlgItem(IDC_OPENGL)->GetWindowRect(rect3);                                             /
 ScreenToClient(rect3);
parent = (CWnd*) GetDlgItem(IDC_OPENGL)->GetParent();

Create(rect3,parent); // i tried using Create(rect3, this);

...

}

void Create(CRect rect, CWnd *parent)
{
    CString className = AfxRegisterWndClass(
        CS_HREDRAW | CS_VREDRAW | CS_OWNDC,
        NULL,
        (HBRUSH)GetStockObject(BLACK_BRUSH),
        NULL);

    CreateEx(
        0,
        className,
        "OpenGL",
        WS_CHILD | WS_VISIBLE | WS_CLIPSIBLINGS | WS_CLIPCHILDREN,
        rect,
        parent,
        0);  

}

However the CreateEx fails and Debug Assertion Failed window pops up (...\src\mfc\wincore.cpp). My initial guess that it is problem with the pointer to the parent dialog box.

Once I comment the CreateEx inside the Create function, everything works fine.

 Can anybody please help me?