System.Web.UI.DataVisualization.Charting missing error in .net 4.0?
<p>I'm trying to use the Chart control in asp.net 4.0.  While I know it required a separate install as part of 3.5, it's included by default with 4.0.</p>

<p>I can see the Chart control in my toolbox, and I can drag it to my designer and see a preview of the chart.  However, when I try to compile my website, I get an error stating:</p>

<pre><code>The type or namespace name 'DataVisualization' does not exist in the namespace 'System.Web.UI' (are you missing an assembly reference?)
</code></pre>

<p>I receive the same error when I take a brand new page and add the following:</p>

<pre><code>using System.Web.UI.DataVisualization;
</code></pre>

<p>Any ideas?  I can understand why I would get this error in 3.5, but no clue why I would receive in 4.0, especially when I can see the control in the toolbox.</p>
