CXTPTabClientWnd + MDI + scrollbar

Thats my sample code:
/* cut */
....
m_wndTabClient.Attach(this, FALSE );
....
....
    SCROLLINFO si;
    si.fMask = SIF_PAGE | SIF_RANGE | SIF_POS;
    si.nMin = 0;
    si.nMax = 100;
    si.nPos = m_nVScrollPos;
    si.nPage = m_nVPageSize;
    m_wndTabClient.SetScrollInfo(SB_VERT, &si, TRUE);
....
/* end */

When i click on my Vertical Scrollbar its vanish. I was trying trough m_wndTabClient.ModifyStyle(0, WS_VSCROLL); but its dont help me and crushing my app. I want to moving my windows on my workspace, so when bottom of window goes under CXTPTabClientWnd space, i want to show my Scrollbar but he is still vanish. Could any one help me with it ?

/* Sorry for my english */