使用加速计时出现未经授权的访问异常

每次用户摇动windows phone设备时，我都会尝试在页面之间导航，但每次更改轴时，都会显示未经授权的访问异常

    public Welcome_2()
    {
        InitializeComponent();
            Accelerometer acc = new Accelerometer();
            acc.TimeBetweenUpdates = TimeSpan.FromMilliseconds(5);
            acc.CurrentValueChanged += new EventHandler<SensorReadingEventArgs<AccelerometerReading>>(accEventHandler);
            acc.Start();
    }
    private void accEventHandler(object sender, SensorReadingEventArgs<AccelerometerReading> e)
    {
        Vector3 accelReading = new Vector3();
        accelReading.X = (float)e.SensorReading.Acceleration.X;
        accelReading.Y = (float)e.SensorReading.Acceleration.Y;
        accelReading.Z = (float)e.SensorReading.Acceleration.Z;
        if (accelReading.X > 0 || accelReading.X < 0)
        {
                NavigationService.Navigate(new Uri("/Get_Insert.xaml", UriKind.Relative));
        }
    }