Problrm in using silverlight toolkit 5 controls

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Silverlight

Hi I am working an application that based on Silverlight 5.
Its framework is MVVM and implemented by Prism.
I am using silverlight 5 toolkit too.

in one of my views I using wrapPanel and DateTimePicker from toolkit.

<navigation:Page x:Class="PIPM2.SupervisionSubSystem.Module.View.TestView"
           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:navigation="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Navigation"
           d:DesignWidth="640" d:DesignHeight="480"
           Title="TestView Page" xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk" xmlns:toolkit="http://schemas.microsoft.com/winfx/2006/xaml/presentation/toolkit" xmlns:my="clr-namespace:Silverlight.Controls;assembly=Silverlight.Controls" xmlns:my1="clr-namespace:Silverlight.Controls.Primitives;assembly=Silverlight.Controls">
    <Grid>
        <sdk:DatePicker  />
        <toolkit:WrapPanel >
        </toolkit:WrapPanel>
    </Grid>
</navigation:Page>

This sample buid successed but at runtime in InitializeComponent() method I got this Error =>

Could not load file or assembly 'System.Windows.Controls.Toolkit, Version=5.0.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The requested assembly version conflicts with what is already bound in the app domain or specified in the manifest. (Exception from HRESULT: 0x80131053)

If I delete one of controls, wrapPanel or DatePicker my Error do not occur again.

please help me.
How can I solve this problem.

thanks a lot.