CFileDialog::DoModal() never returns

I am encountering a wierd error, and I can't figure out which way to turn.
Something deep within the call tree of CFileDialog::DoModal() is (apparently)
failing, causing the dialog to never be displayed, and the f() never to
return. Here's the failing code:

void CPvtDlg::OnBnClickedBnFileBd()
{
        
    // specify a file
    CFileDialog fileOpenBox ( TRUE,
// BOOL bOpenFileDialog
                                NULL,
// LPCTSTR lpszDefExt
                                NULL,
// LPCTSTR lpszFileName
                                (OFN_HIDEREADONLY | OFN_OVERWRITEPROMPT),
// DWORD dwFlags
                                NULL, // LPCTSTR lpszFilter
                                NULL );
// CWnd* pParentWnd
    
    // extract file name
    if( IDOK == fileOpenBox.DoModal() )
    {
        m_strFileNameBd = fileOpenBox.GetFileName();
        m_strPathNameBd = fileOpenBox.GetPathName();
    }
....

Single stepping, I am unable to step over the DoModal() call. Stepping into
the call to DoModal(), I find myself inside dlgfile.cpp:

INT_PTR CFileDialog::DoModal()
{
    ASSERT_VALID(this);
    ASSERT(m_ofn.Flags & OFN_ENABLEHOOK);
    ASSERT(m_ofn.lpfnHook != NULL); // can still be a user hook

    // zero out the file buffer for consistent parsing later
    ASSERT(AfxIsValidAddress(m_ofn.lpstrFile, m_ofn.nMaxFile));
    DWORD nOffset = lstrlen(m_ofn.lpstrFile)+1;
    ASSERT(nOffset <= m_ofn.nMaxFile);
    memset(m_ofn.lpstrFile+nOffset, 0, (m_ofn.nMaxFile-nOffset)*sizeof(TCHAR));

    // This is a special case for the file open/save dialog,
    // which sometimes pumps while it is coming up but before it has
    // disabled the main window.
    HWND hWndFocus = ::GetFocus();
    BOOL bEnableParent = FALSE;
    m_ofn.hwndOwner = PreModal();
    AfxUnhookWindowCreate();
    if (m_ofn.hwndOwner != NULL && ::IsWindowEnabled(m_ofn.hwndOwner))
    {
        bEnableParent = TRUE;
        ::EnableWindow(m_ofn.hwndOwner, FALSE);
    }

    _AFX_THREAD_STATE* pThreadState = AfxGetThreadState();
    ASSERT(pThreadState->m_pAlternateWndInit == NULL);

    if (m_ofn.Flags & OFN_EXPLORER)
        pThreadState->m_pAlternateWndInit = this;
    else
        AfxHookWindowCreate(this);

    INT_PTR nResult;
    if (m_bOpenFileDialog)
        nResult = ::AfxCtxGetOpenFileName(&m_ofn);
    else
        nResult = ::AfxCtxGetSaveFileName(&m_ofn);
....
I am unable to step over the call to ::AfxCtxGetOpenFileName(&m_ofn); in the
if branch above. Stepping into it allows me to step through

OPENFILENAME& CFileDialog::GetOFN()
{
    return *m_pOFN;
}

and

COMMDLG_AFXCTXFUNC(BOOL,GetOpenFileNameW,(LPOPENFILENAMEW
unnamed1),(unnamed1))

to

AFX_MODULE_STATE* AFXAPI AfxGetModuleState()
{
    _AFX_THREAD_STATE* pState = _afxThreadState;
    ENSURE(pState);
    AFX_MODULE_STATE* pResult;
    if (pState->m_pModuleState != NULL)
    {
        // thread state's module state serves as override
        pResult = pState->m_pModuleState;
    }
    else
    {
        // otherwise, use global app state
        pResult = _afxBaseModuleState.GetData();
    }
    ENSURE(pResult != NULL);
    return pResult;
}

back through

COMMDLG_AFXCTXFUNC(BOOL,GetOpenFileNameW,(LPOPENFILENAMEW
unnamed1),(unnamed1))

I could probably continue, but it seems to me that I am inside the innards
of an area of the libs that I have no business in. What is it up in the API
level that I am screwing up?