Android : vuforia activate dataset at runtime

I'm trying to activate a dataset that I read from external storage at runtime. I'm using the following code to do that and I've put it in onQCarUpdaate method in VideoPlayback.java:

TrackerManager trackerManager = TrackerManager.getInstance();
ImageTracker imageTracker = (ImageTracker) trackerManager
            .getTracker(ImageTracker.getClassType());

    if (imageTracker == null)
    {
        Log.d(
                LOGTAG,
                "Failed to load tracking data set because the ImageTracker has not been initialized.");
        result = false;
    }

    imageTracker.stop();
    // Create the data sets:
    dataSetStonesAndChips = imageTracker.createDataSet();
    if (dataSetStonesAndChips == null)
    {
        Log.d(LOGTAG, "Failed to create a new tracking data.");
        result = false;
    }
    // Load the data sets:
    if (!dataSetStonesAndChips.load(mTrackersDataPath,
            STORAGE_TYPE.STORAGE_ABSOLUTE))
    {
        Log.d(LOGTAG, "Failed to load data set.");
        result = false;
    }

    // Activate the data set:
    if (!imageTracker.activateDataSet(dataSetStonesAndChips))
    {
        Log.d(LOGTAG, "Failed to activate data set.");
        result = false;
    }
    Log.d(LOGTAG, "Successfully loaded and activated data set.");

boolean wasActivate = (imageTracker.getActiveDataSet() == dataSetStonesAndChips);
int count = imageTracker.getActiveDataSetCount();

My problem is that wasActiated is false eventhough count is equal to 1. I tried getting the active dataset by index but nothing changed. If I put this code in doLoadTrackersData method then wasActivated is true but not here.

Also the dataset is infact correctly activated since the application works fine but to unload the dataset I need to fix this problem. Right now if I try deactivating and destroying the dataset my app crashes.