title: System.Web.UI.DataVisualization.Charting.Grid exists twice in GAC
body: <p>I've upgraded a web application from .NET 3.5 to .NET 4, and I get this exception when browsing to a page that uses the Chart control:</p>
  
  <blockquote>
    <p>The type 'System.Web.UI.DataVisualization.Charting.Grid' exists in both 'c:\Windows\Microsoft.NET\assembly\GAC_MSIL\System.Web.DataVisualization\v4.0_4.0.0.0__...\System.Web.DataVisualization.dll' and 'c:\Windows\assembly\GAC_MSIL\System.Web.DataVisualization\3.5.0.0__...\System.Web.DataVisualization.dll'</p>
  </blockquote>
  
  <p>How can I get this working, using the 4.0 control?  Thanks.</p>