Windows Phone ExpanderView - "The parameter is incorrect." - windows-phone-7.1

Question

I am trying to make a "TreeView-like" display in my Windows Phone (7.1) application.
In order to do this, I am using the "ExpanderView" in the Silverlight Toolkit.
So basically, my program adds ExpanderViews inside ExpanderViews in order to create the tree.
Everything is fin until an element exceeds the screen horizontally, where it gives me the exception "The parameter is incorrect." on the "Debugger.Break()" line in the following code:
// Code to execute on Unhandled Exceptions
private void Application_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e)
{
if (System.Diagnostics.Debugger.IsAttached)
{
// An unhandled exception has occurred; break into the debugger
System.Diagnostics.Debugger.Break();
}
}
Under App.xaml.cs.
I am assuming the element doesn't initialize/load corrently, as I had this exception before with the same element, where I was adding items without the parent element being fully loaded.
This is my XAML:
<Grid x:Name="LayoutRoot" Background="Transparent">
<Grid x:Name="ContentPanel" Margin="12,0,12,0"/>
</Grid>
<phone:PhoneApplicationPage.ApplicationBar>
<shell:ApplicationBar IsVisible="True" IsMenuEnabled="True">
<shell:ApplicationBarIconButton IconUri="/Images/Plus.png" Text="Add" Click="ApplicationBarIconButtonClick"/>
</shell:ApplicationBar>
</phone:PhoneApplicationPage.ApplicationBar>
And this is the code behind:
public MainPage()
{
InitializeComponent();
_lastView = new ExpanderView { Header = "Header", IsExpanded = true };
ContentPanel.Children.Add(_lastView);
}
private ExpanderView _lastView;
private void ApplicationBarIconButtonClick(object sender, System.EventArgs e)
{
var newItem = new ExpanderView {Header = "Header", IsExpanded = true};
_lastView.Items.Add(newItem);
_lastView = newItem;
}
The very next time I click the application bar button (when the next element exceeds the screen horizontally), it gives me the exception:

Answer 1

Check last Visual Studio updates. I had same problem before NuGet package update. Restart of Vissual Studio + update helped me