UIAutomation: AddAutomationEventHandler() возвращает E_INVALIDARG

Вот мой код:

// Defines an event handler for general UI Automation events. It listens for
// tooltip and window creation and destruction events. 
#include <windows.h>
#include <stdio.h>
#include <UIAutomation.h>

class EventHandler :
    public IUIAutomationEventHandler
{
private:
    LONG _refCount;

public:
    int _eventCount;

    // Constructor.
    EventHandler() : _refCount(1), _eventCount(0)
    {
    }

    // IUnknown methods.
    ULONG STDMETHODCALLTYPE AddRef()
    {
        ULONG ret = InterlockedIncrement(&_refCount);
        return ret;
    }

    ULONG STDMETHODCALLTYPE Release()
    {
        ULONG ret = InterlockedDecrement(&_refCount);
        if (ret == 0)
        {
            delete this;
            return 0;
        }
        return ret;
    }

    HRESULT STDMETHODCALLTYPE QueryInterface(REFIID riid, void** ppInterface)
    {
        if (riid == __uuidof(IUnknown))
            *ppInterface = static_cast<IUIAutomationEventHandler*>(this);
        else if (riid == __uuidof(IUIAutomationEventHandler))
            *ppInterface = static_cast<IUIAutomationEventHandler*>(this);
        else
        {
            *ppInterface = NULL;
            return E_NOINTERFACE;
        }
        this->AddRef();
        return S_OK;
    }

    // IUIAutomationEventHandler methods
    HRESULT STDMETHODCALLTYPE HandleAutomationEvent(IUIAutomationElement * pSender, EVENTID eventID)
    {
        _eventCount++;
        switch (eventID)
        {
        case UIA_AutomationFocusChangedEventId:
            wprintf(L">> Event FocusChanged Received! (count: %d)\n", _eventCount);
            break;
        case UIA_ToolTipOpenedEventId:
            wprintf(L">> Event ToolTipOpened Received! (count: %d)\n", _eventCount);
            break;
        case UIA_ToolTipClosedEventId:
            wprintf(L">> Event ToolTipClosed Received! (count: %d)\n", _eventCount);
            break;
        case UIA_Window_WindowOpenedEventId:
            wprintf(L">> Event WindowOpened Received! (count: %d)\n", _eventCount);
            break;
        case UIA_Window_WindowClosedEventId:
            wprintf(L">> Event WindowClosed Received! (count: %d)\n", _eventCount);
            break;
        default:
            wprintf(L">> Event (%d) Received! (count: %d)\n", eventID, _eventCount);
            break;
        }
        return S_OK;
    }
};

int main(int argc, char* argv[])
{
    HRESULT hr;
    int ret = 0;
    IUIAutomationElement* pTargetElement = NULL;
    EventHandler* pEHTemp = NULL;

    CoInitializeEx(NULL, COINIT_MULTITHREADED);
    IUIAutomation* pAutomation = NULL;
    hr = CoCreateInstance(__uuidof(CUIAutomation), NULL, CLSCTX_INPROC_SERVER, __uuidof(IUIAutomation), (void**)&pAutomation);
    if (FAILED(hr) || pAutomation == NULL)
    {
        ret = 1;
        goto cleanup;
    }
    // Use root element for listening to window and tooltip creation and destruction.
    hr = pAutomation->GetRootElement(&pTargetElement);
    if (FAILED(hr) || pTargetElement == NULL)
    {
        ret = 1;
        goto cleanup;
    }

    pEHTemp = new EventHandler();
    if (pEHTemp == NULL)
    {
        ret = 1;
        goto cleanup;
    }

    wprintf(L"-Adding Event Handlers.\n");
    hr = pAutomation->AddAutomationEventHandler(UIA_ToolTipOpenedEventId, pTargetElement, TreeScope_Subtree, NULL, (IUIAutomationEventHandler*)pEHTemp);
    if (FAILED(hr))
    {
        ret = 1;
        goto cleanup;
    }
    hr = pAutomation->AddAutomationEventHandler(UIA_ToolTipClosedEventId, pTargetElement, TreeScope_Subtree, NULL, (IUIAutomationEventHandler*)pEHTemp);
    if (FAILED(hr))
    {
        ret = 1;
        goto cleanup;
    }
    hr = pAutomation->AddAutomationEventHandler(UIA_Window_WindowOpenedEventId, pTargetElement, TreeScope_Subtree, NULL, (IUIAutomationEventHandler*)pEHTemp);
    if (FAILED(hr))
    {
        ret = 1;
        goto cleanup;
    }
    hr = pAutomation->AddAutomationEventHandler(UIA_Window_WindowClosedEventId, pTargetElement, TreeScope_Subtree, NULL, (IUIAutomationEventHandler*)pEHTemp);
    if (FAILED(hr))
    {
        ret = 1;
        goto cleanup;
    }
    // Error is here. hr returns E_INVALIDARG.
    hr = pAutomation->AddAutomationEventHandler(UIA_AutomationFocusChangedEventId, pTargetElement, TreeScope_Subtree, NULL, (IUIAutomationEventHandler*)pEHTemp);
    if (FAILED(hr))
    {
        ret = 1;
        goto cleanup;
    }

    wprintf(L"-Press any key to remove event handlers and exit\n");
    getchar();

    wprintf(L"-Removing Event Handlers.\n");

cleanup:
    // Remove event handlers, release resources, and terminate
    if (pAutomation != NULL)
    {
        hr = pAutomation->RemoveAllEventHandlers();
        if (FAILED(hr))
            ret = 1;
        pAutomation->Release();
    }

    if (pEHTemp != NULL)
        pEHTemp->Release();

    if (pTargetElement != NULL)
        pTargetElement->Release();

    CoUninitialize();
    return ret;
}

Этот код взят из примеров от Microsoft о реализации классов событий для UIAutomation.

Я немного отредактировал код, чтобы он мог поддерживать события Focus, но мне не удалось инициализировать одну строку кода.

Я не понимаю, почему hr = pAutomation->AddAutomationEventHandler(UIA_AutomationFocusChangedEventId, pTargetElement, TreeScope_Subtree, NULL, (IUIAutomationEventHandler*)pEHTemp) возвращает E_INVALIDARG.

Пробовал читать документы, и я не могу найти причину.

Пожалуйста помоги.