How to pop up childwindow in Model?

I am working in silverlight5 and i had to display a error messagebox(made by me using childwindow).I using MVVM approach and problem is situation is like this that i have to to pop up that error message in Model class when something go wrong.

I do this by doing ( cfw.Show()) in model class:

public static void ShowSmallMessageWithResult(string message) 
{
    ConfirmationWindow cfw = new ConfirmationWindow();
    cfw.SetMessage(message);
    cfw.Show();
}

The problem is do not pop any error messagebox (i mean this chiildwindow). I dont know why ?

Note: Please note that ConfirmationWindow.xaml is in Model folder.

Why it is not working? How to make it work ?

And ConfirmationWindow.xaml is :

<silvercontrols:ChildWindow x:Class="Model.MessageFolder.ConfirmationWindow"
           xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
           xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
           xmlns:silvercontrols="clr-namespace:Silverlight.Windows.Controls;assembly=Silverlight.Windows.Controls"
           xmlns:controls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls"
          xmlns:toolkit="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Toolkit"
           Title="Message" Width="Auto" Height="Auto" MouseRightButtonDown="ChildWindow_MouseRightButtonDown"><silvercontrols:ChildWindow.Style><StaticResource ResourceKey="MessageBoxStyle"/></silvercontrols:ChildWindow.Style><Grid x:Name="LayoutRoot" MinWidth="360"><StackPanel Orientation="Vertical"><TextBlock x:Name="MessageBox" Margin="10 15 0 0" Height="Auto" FontSize="12" Text="Text" Foreground="White" TextWrapping="Wrap" HorizontalAlignment="Left" /><StackPanel x:Name="ContentBox" Margin="10 15 0 0" Height="Auto" Orientation="Horizontal"></StackPanel><StackPanel Margin="0 0 0 10" Orientation="Horizontal" HorizontalAlignment="Center" Height="45"><Button x:Name="YesBtn" Content="Yes" Width="82" HorizontalAlignment="Left" VerticalAlignment="Bottom" Style="{StaticResource ButtonStyle_Blue}"/><Button x:Name="NoBtn" Content="No" Margin="60 0 0 0" Width="82" HorizontalAlignment="Right" VerticalAlignment="Bottom" Style="{StaticResource ButtonStyle_Blue}"/></StackPanel></StackPanel></Grid></silvercontrols:ChildWindow>

and ConfirmationWindow.xaml.cs is :

using System.Windows;   
namespace Model.MessageFolder
{
    public partial class ConfirmationWindow : Silverlight.Windows.Controls.ChildWindow
    {
        private bool showBtnClose;
        public ConfirmationWindow(bool showBtnClose = false)
        {
            InitializeComponent();
            HasCloseButton = showBtnClose;
            this.showBtnClose = showBtnClose;
            NoBtn.Click += Close;
        }

        #region METHODS
        public void SetMessage(string message)
        {
            MessageBox.Text = message;
        }
        public void AddContent(UIElement elt)
        {
            ContentBox.Children.Add(elt);
        }
        #endregion

        #region EVENT_HANDLER
        public void Close(object sender, RoutedEventArgs e)
        {
            this.Close();
        }
        #endregion

        private void ChildWindow_MouseRightButtonDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            e.Handled = true;
        }
    }
}

The problem is do not pop any error messagebox (i mean this chiildwindow). I dont know why ?

Note: Please note that ConfirmationWindow.xaml is in Model folder. I know its not a good idea but there are no more option left because its a big already existing project and i have no more options left then popuping error message childwindow  in model 

Why it is not working? How to make it work ?