After numerous tries, we finally solved the problem. I am writing this because hopefully will help somebody else.

 The build machine automatically increase de version of the assemblies. Apparently, the license mechanism uses this. Therefore, although we did not make any changes to our Silverlight projects, the license will be invalid. We made a work around by not increasing anymore the assembly version of the Silverlight projects.

 It is disappointing that there is not any documentation about this and we found this by trial & error. A licensing console utility that could be integrated in the build scripts will be greatly appreciated. We have a lot of builds (release, testing, nightly) & configurations and manual generation is just a loss of time.

Hello,

It partialy worked. I had to add this

private void OnClosed( object sender, ISRoutedEventArgs args )
      {
         if ( (sender as UXPopup).Name == "PickerPopup" )
         {
            args.Handled = true;
         }
      }

because the stack button would remain pressed when you click outside of the two popups and you have to click it twice to open his popup again.

I found another problem: when the UXPopup control must be repositioned because of the screen limits, the arrow of the callout of the UXStackButton is moved from the button to a side. I've attached pictures to show this bug.

I wanted to add that we finally upgraded to ClientUI 5, but the problems remained (the exeption if the browser is not resized too).

Sorry for the delay, but I had to finish the task and did not have time to reply.

I've managed to create a simple example to reporduce the bug:

<Intersoft:UXPage 
	xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
	xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
	xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
	xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
	mc:Ignorable="d"
	xmlns:Intersoft="http://intersoft.clientui.com/schemas"
	x:Class="ClientUIApplication1.MainPage" 
	Title="MainPage Page"
	d:DesignWidth="640" d:DesignHeight="480">
	
	<Grid x:Name="LayoutRoot">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"></ColumnDefinition>
            <ColumnDefinition Width="50"></ColumnDefinition>
            <ColumnDefinition Width="*"></ColumnDefinition>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="50"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
        </Grid.RowDefinitions>
        <Intersoft:UXStackButton Content="Open Settings" DisplayMode="Content"  StackMode="GridStyle" Grid.Row="1" Grid.Column="1">
            <Intersoft:UXStackButton.StackGridTemplate>
                <DataTemplate>
                    <StackPanel Width="250">                       
                        <Intersoft:GlassButton Content="Open Popup" Margin="4" Click="GlassButton_Click"/>
                        <Intersoft:UXPopup x:Name="PickerPopup" DisableOverlay="True" DisplayAnimation="Zoom" PreferredPosition="BottomLeft" VerticalAlignment="Top" IsOpen="{Binding IsPopupOpen, Mode=TwoWay}" >
                            <StackPanel Margin="20">
                                <Button Content="Close" Click="Button_Click"></Button>
                            </StackPanel>
                        </Intersoft:UXPopup>
                    </StackPanel>
                </DataTemplate>
            </Intersoft:UXStackButton.StackGridTemplate>
        </Intersoft:UXStackButton>
    </Grid>
</Intersoft:UXPage>

 and the code behind:

using System.ComponentModel;
using System.Windows;
using Intersoft.Client.UI.Navigation;
namespace ClientUIApplication1
{
   public partial class MainPage: UXPage, INotifyPropertyChanged
   {
      /// <summary>
      /// RaisePropertyChanged
      /// </summary>
      /// <param name="sPropertyName"></param>
      protected void RaisePropertyChanged( string sPropertyName )
      {
         if ( PropertyChanged != null )
         {
            PropertyChanged( this, new PropertyChangedEventArgs( sPropertyName ) );
         }//if
      }//RaisePropertyChanged
      public event PropertyChangedEventHandler PropertyChanged;
      private bool m_isPopupOpen;
      public bool IsPopupOpen
      {
         set
         {
            m_isPopupOpen = value;
            RaisePropertyChanged( "IsPopupOpen" );
         }
         get
         {
            return m_isPopupOpen;
         }
      }
      public MainPage()
      {
         InitializeComponent();
         LayoutRoot.DataContext = this;
      }
      private void GlassButton_Click( object sender, RoutedEventArgs e )
      {
         IsPopupOpen = true;
         
      }
      private void Button_Click( object sender, RoutedEventArgs e )
      {
         IsPopupOpen = false;
      }
   }
}

 Also, a strange bug appears: if the browser window is not resized, the app crashes with null reference exception when you click the stack button.