Found not working imports: QtMultimedia is not installed

Czarek

import QtQuick 2.6
import QtQuick.Controls 1.5
import QtQuick.Dialogs 1.2
import QtMultimedia 5.6
import QtQuick.Layouts 1.3

Item {
    width: 640
    height: 360

    Camera {
        id: camera

        imageProcessing.whiteBalanceMode: CameraImageProcessing.WhiteBalanceFlash

        exposure {
            exposureCompensation: -1.0
            exposureMode: Camera.ExposurePortrait
        }

        flash.mode: Camera.FlashRedEyeReduction

        imageCapture {
            onImageCaptured: {
                photoPreview.source = preview  // Show the preview in an Image
            }
        }
    }

    VideoOutput {
        source: camera
        anchors.fill: parent
        focus : visible // to receive focus and capture key events when visible
    }

    Image {
        id: photoPreview
    }
}

I just uinstalled Qt 5.5.1 and installed Qt 5.6 (but above is the new project created in Qt 5.6). I added
QT += multimedia
in my pro file. I use MSVC 2013 (as alway when using Qt), Windows 7. It builds program and when I click Run, it works, although it shows in Application Output: 3x failed to access to the graph builder. I could ignore it, but I am not able to access to Design mode ("Cannot open this QML document beacuse of an error in the QML file"). Could you help me to solve it?