title: Could not load file or assembly WPFToolkit
body: <p>I am trying to use WPFToolkit in my user control dll. I inserted the WPFToolkit in its reference, and my user control dll builds with no error. 
  Then I insert my user control dll into my application, but when my application new an object of my user control dll</p>
  
  <pre><code>  MultiROIStats mroi = new MultiROIStats();
  </code></pre>
  
  <p>the exception occured, saying:</p>
  
  <p><strong>Additional information: Could not load file or assembly 'WPFToolkit, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.</strong> </p>
  
  <p>Here is my user control dll code, the constructor where the error occurs.</p>
  
  <p>View xaml code:</p>
  
  <pre><code>&lt;Window x:Class="MultiROIStats.MultiROIStats"
               xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
               xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
               xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
               xmlns:d="http://schemas.microsoft.com/expression/blend/2008"    
               xmlns:dg="http://schemas.microsoft.com/wpf/2008/toolkit"              
               mc:Ignorable="d" 
               d:DesignHeight="300" d:DesignWidth="300"&gt;
      &lt;Grid&gt;
          &lt;dg:DataGrid ItemsSource="{Binding Path=FileData}" Margin="0,30,0,0" /&gt;
          &lt;Button Height="22" HorizontalAlignment="Left" Margin="8,4,0,0"
              Name="button1" VerticalAlignment="Top" Width="48"
              Command="{Binding Path=GetDataCommand}"&gt;Button
          &lt;/Button&gt;
      &lt;/Grid&gt;
  &lt;/Window&gt;
  </code></pre>
  
  <p>View C# code</p>
  
  <pre><code>using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  using System.Threading.Tasks;
  using System.Windows;
  using System.Windows.Controls;
  using System.Windows.Data;
  using System.Windows.Documents;
  using System.Windows.Input;
  using System.Windows.Media;
  using System.Windows.Media.Imaging;
  using System.Windows.Navigation;
  using System.Windows.Shapes;
  
  namespace MultiROIStats
  {
      using System.Windows;
      using ViewModel;
  
      //xmlns:dg="clr-namespace:Microsoft.Windows.Controls;assembly=WpfToolkit"
      /// &lt;summary&gt;
      /// Interaction logic for UserControl1.xaml
      /// &lt;/summary&gt;
      public partial class MultiROIStats : Window
      {
          public MultiROIStats()
          {          
              InitializeComponent();    // exception occurs here!
              DataContext = new MultiROIStatsViewModel();
          }
      }
  }
  </code></pre>
  
  <p>I also checked the binary folder of my user control dll, the WPFToolkei.dll is there. So I am confused, and I am wondering how can I correct this error? Thanks.</p>