Photochooser and OnNavigatedFrom exception

Question

I ran into bizarre problem, hopefully you will be able to give me a hand. I start PhotoChooserTask, choose photo and when it comes back it suddenly throws an exception. Picture below depicts the situation. If I delete code connected with State or change writing object to string it works as expected. I try to find a solution why this error occurs. I'm receiving an error "rootframe_navigation_failed" and "An unhandled exception of type 'System.Runtime.Serialization.InvalidDataContractException' occurred in Microsoft.Phone.Interop.ni.dll". When PhotoChoser is invoked onNavigatedFrom is launched and then it stops, but why? Image assigning seems to be correct.

Unfortunately that has nothing in common with Image. I made simple class as I could and error still takes place but when I get rid of photochooser task and for instance put into gallery method navigation to another page there is no problem so I presume that problem results from photochoosertask. But why this happens, still trying to find out.

public partial class Page1 : PhoneApplicationPage
{
    private PhotoChooserTask photo_chooser;

    public Page1()
    {
        InitializeComponent();


    }

    private void gallery(object sender, RoutedEventArgs e)
    {
         photo_chooser = new PhotoChooserTask();
         photo_chooser.Show();
         photo_chooser.Completed += photo_chooser_Completed;
    }


    void photo_chooser_Completed(object sender, PhotoResult e)
    {
        switch (e.TaskResult)
        {
            case TaskResult.OK:
                {
                    break;
                }
        }
    }


    protected override void OnNavigatingFrom(NavigatingCancelEventArgs e)
    {
        PhoneApplicationService.Current.State["sth"] = new Rect();
        base.OnNavigatingFrom(e);
    }

}