title: Cannot get the WPFToolkit chart to show data (throws an exception)
body: <p>After a few hours of unsuccessful attempts, I hope someone helps me here. I followed a post showing how to simply display data in WPFToolkit lineChart:</p>
  
  <p>So I have the chart:</p>
  
  <pre><code>&lt;chartingToolkit:Chart x:Name="myChart" Title="Power Graph" Background="YellowGreen" 
                               Foreground="DarkBlue" VerticalAlignment="Top" Margin="16,36,20,0" Height="432"  IsEnabled="True"&gt;
                  &lt;chartingToolkit:LineSeries Title="SolarCell"  
                                      ItemsSource="{Binding}" 
                                      DependentValueBinding="{Binding Path=Value}" 
                                      IndependentValueBinding="{Binding Path=Key}"
                                      IsSelectionEnabled="True"&gt;
                      &lt;chartingToolkit:LineSeries.IndependentAxis&gt;
                          &lt;chartingToolkit:LinearAxis Orientation="X" Title="Time (Mins)" Interval="5"  /&gt;
                      &lt;/chartingToolkit:LineSeries.IndependentAxis&gt;
                      &lt;chartingToolkit:LineSeries.DependentRangeAxis&gt;
                          &lt;chartingToolkit:LinearAxis Orientation="Y" Title="Power (W)"/&gt;
                      &lt;/chartingToolkit:LineSeries.DependentRangeAxis&gt;
                  &lt;/chartingToolkit:LineSeries&gt;
              &lt;/chartingToolkit:Chart&gt;
  </code></pre>
  
  <p>and the C# code:</p>
  
  <pre><code>Dictionary&lt;string, float&gt; a = new Dictionary&lt;string, float&gt;();
  this.myChart.DataContext = a;
  
  void timer_Tick(object sender, EventArgs e)
          {
              this.a.Add(this.elapsedTime.ToString(),meter.GetResult());
             elapsedTime++;
  
          }
  </code></pre>
  
  <p>When run, I got the following exception:</p>
  
  <blockquote>
    <p>An unhandled exception of type 'System.InvalidOperationException'
    occurred in System.Windows.Controls.DataVisualization.Toolkit.dll</p>
    
    <p>Additional information: Assigned independent axis cannot be used. This
    may be due to an unset Orientation property for the axis.</p>
  </blockquote>