Can't register a Time triggered Background Task

For a Windows 8 App, in C#/Xaml I try to register a background task. It's hard to tell but I guess my background task is well registred but when I click on the name of my background task on the Debug Location Toolbar my app stops working without any message.

I looked at the log on the Event Viewer and I get : "The background task with entry point MyApp.Pages.SampleBackgroundTask and name Example hourly background task failed to activate with error code 0x80010008."

Here is my code :

   private async void Button_Click_BackgroundTask(object sender, RoutedEventArgs e)
    {
        string entryPoint = "MyApp.Pages.SampleBackgroundTask";
        string taskName = "Example hourly background task";
        TimeTrigger hourlyTrigger = new TimeTrigger(60, false);

        BackgroundTaskRegistration myBackGroundTaskRegistration =   RegisterBackgroundTask(entryPoint, taskName, hourlyTrigger, null);
        if(myBackGroundTaskRegistration != null)
        AttachProgressAndCompletedHandlers(myBackGroundTaskRegistration);
    }


   public static BackgroundTaskRegistration RegisterBackgroundTask(String taskEntryPoint,
                                                                    String name,
                                                                    IBackgroundTrigger trigger,
                                                                    IBackgroundCondition condition)
    {

        var taskRegistered = false;
        var iter = Windows.ApplicationModel.Background.BackgroundTaskRegistration.AllTasks;

        foreach (var item in iter)
        {
            var task = item.Value;
            if (task.Name == name)
            {
                taskRegistered = true;
                return item.Value as BackgroundTaskRegistration;
            }
        }


        var builder = new BackgroundTaskBuilder();

        builder.Name = name;
        builder.TaskEntryPoint = taskEntryPoint;
        builder.SetTrigger(trigger);

        if (condition != null)
        {

            builder.AddCondition(condition);
        }

        BackgroundTaskRegistration taskBack = builder.Register();

        return taskBack;
    }


       private void AttachProgressAndCompletedHandlers(IBackgroundTaskRegistration task)
    {
        task.Progress += new BackgroundTaskProgressEventHandler(OnProgress);
        task.Completed += new BackgroundTaskCompletedEventHandler(OnCompleted);
    }


  private void OnProgress(IBackgroundTaskRegistration task, BackgroundTaskProgressEventArgs args)
    {
        var progress = "Progress: " + args.Progress + "%";

    }


    private void OnCompleted(IBackgroundTaskRegistration task, BackgroundTaskCompletedEventArgs args)
    {
        Debug.WriteLine("Hi");
    }

I added this in the manifest :

      <Extension Category="windows.backgroundTasks" EntryPoint="MyApp.Pages.SampleBackgroundTask">
      <BackgroundTasks>
        <Task Type="timer" />
      </BackgroundTasks>
    </Extension>

Did I forget something?

Thank you for your help.

EDIT : here is the code of my Task, within one of my project page :

      public sealed class SampleBackgroundTask : IBackgroundTask
{
    public void Run(IBackgroundTaskInstance taskInstance)
    {
        BackgroundTaskDeferral _deferral = taskInstance.GetDeferral();

        _deferral.Complete();
    }
}

I had this problem too. I also had mine in the same project. I finally got it to work by moving the task into a separate project. I had to set the project output as windows runtime component(under properties applicaiton tab) . Also don't forget to add the project as a reference.