UpdateSourceTrigger=PropertyChanged causing exception during InitializeComponent() on WP7

I have a simple page with just one TextBox control whose Text is bound to a property in my ViewModel. When I use UpdateSourceTrigger=Default, everything is fine, however, when I use UpdateSourceTrigger=PropertyChanged, I get an exception

{Failed to create a 'System.Windows.Data.UpdateSourceTrigger' from the text 'PropertyChanged'.}

When I click on the details of the exception, I get

{"You can only use State between OnNavigatedTo and OnNavigatedFrom"}

I am suspecting that this is because I set the DataContext for the binding in the NavigatedTo() function that is called AFTER the InitializeComponent() where the exception is thrown.

Any suggestions on how to get around this -- I really need the PropertyChanged trigger behavior.

Thanks.

Here are the 2 functions and XAML code for completeness:

public AddNewPlayerPage()
{
    InitializeComponent();
}
protected override void OnNavigatedTo(NavigationEventArgs e)
{
    base.OnNavigatedTo(e);
    if (_viewModel == null)
    {
        _viewModel = PhoneApplicationService.Current.State["ChooseItemVM"] as ChooseItemVM;
        DataContext = _viewModel;
    }
}

<TextBox Text="{Binding Name, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>