Is there anything wrong in this piece of code?

Code:
void CreateToolTip(HWND hwndParent, RECT rectTip, LPWSTR lpTipString){
    HWND hwndTT = CreateWindowEx(WS_EX_TOPMOST,
		TOOLTIPS_CLASS, NULL,
        WS_POPUP | TTS_NOPREFIX | TTS_ALWAYSTIP,		
        CW_USEDEFAULT, CW_USEDEFAULT,
        CW_USEDEFAULT, CW_USEDEFAULT,
        hwndParent, NULL, hInst,NULL);

    SetWindowPos(hwndTT, HWND_TOPMOST, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE | SWP_NOACTIVATE);

    TOOLINFO ti = { 0 };
    ti.cbSize = sizeof(TOOLINFO);
    ti.uFlags = TTF_SUBCLASS|TTF_IDISHWND;
    ti.hwnd = hwndParent;
    ti.hinst = hInst;
    ti.lpszText = lpTipString;
    ti.rect = rectTip;

    SendMessage(hwndTT, TTM_ADDTOOL, 0, (LPARAM) (LPTOOLINFO) &ti);	
}
I call this function in my WM_CREATE / WM_INITDIALOG, but I never see a tooltip if
the mouse hovers the rect. I do call InitCommonControlsEx() before.

?