title: Silverlight charting toolkit: Generated LineSeries throws Exception
body: <p>I have the following problem:<br>
  In our application we have a list of reports with sub categories defined at runtime...<br>
  The overall results of the report are shown in a ColumnSeries, which works fine. Now I have to show the results of the sub categories in a LineSeries for direct comparison, which won't work.
  This is what I have so far (in code behind):</p>
  
  <pre><code>foreach (var item in ReportListViewModel.ReportSections)
  {
      var series = new LineSeries();
      series.SetBinding(DataPointSeries.ItemsSourceProperty, new Binding("ItemList"));
      series.IndependentValuePath = "Date";
      series.DependentValuePath = item.BindingPath; // points to an existing entry in a Dictionary&lt;string, double&gt;
      series.Title = item.Text;
      chart.Series.Add(series);
  }
  </code></pre>
  
  <p>It works fine, but once the data is loaded, I get a InvalidOperationException stating that no suitable axis for plotting the values is found.</p>
  
  <p>The following works totally fine (even though it isn't exactly what I need):</p>
  
  <pre><code>foreach (...)
  {
      ...
      series.DependentValuePath = "Result" // Result is the dependent property of the ColumnSeries, and I tested it just to make sure it isn't me
      ...
  }
  </code></pre>