Wednesday, 9 November 2011

Error executing child request for ChartImg.axd when Rendering a Custom Charting WebPart in SharePoint 2010

 I deployed a custom SharePoint 2010 web part today that uses the Microsoft Chart Controls For ASP.NET 3.5. However, after deployment, I began receiving the following exception when it rendered within an IIS 7 Hosted site (SharePoint 2010 running Windows 7)

Error executing child request for ChartImg.axd

I already had the handler entries set up the same as seen in the code samples. The main problem is that most web.config examples and the official samples don't include the required web.config entries for the ChartImg.axd httphandler (so that they operate correctly in IIS 7 and above).

Windows 7 and Windows Server 2008 use IIS 7 so using the httpHandlers section won’t work like it does in previous versions of IIS – you must instead add an item to the handlers config section of the system.webserver node, like so:

<system.webServer>
    <handlers>
      <add name="ChartImageHandler" preCondition="integratedMode" verb="GET,HEAD,POST" path="ChartImg.axd" type="System.Web.UI.DataVisualization.Charting.ChartHttpHandler, System.Web.DataVisualization, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
    </handlers>
  </system.webServer>

You should also make sure that you are using the POST value in the verb attribute like so:

verb="GET,HEAD,POST".

Once your web application is configured correctly, you should now be able to go to http://SITENAME:PORTNUMBER/Charting.axd and receive a blank screen without any errors. This shows that the charting httphandler is now operational.

Full example of web.config with correct Chart handler entries:
<?xml version="1.0"?>
<configuration>
  <appSettings>
    <add key="ChartImageHandler" value="storage=file;timeout=20;dir=c:\TempImageFiles\;" />
  </appSettings>
  <connectionStrings/>
  <system.web>
    <pages>
      <controls>
        <add tagPrefix="asp" namespace="System.Web.UI.DataVisualization.Charting"
        assembly="System.Web.DataVisualization, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
      </controls>
    </pages>
    <compilation debug="true">
      <assemblies>
        <add assembly="System.Web.DataVisualization, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
        <add assembly="System.Windows.Forms, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
      </assemblies>
    </compilation>
    <httpHandlers>
      <add path="ChartImg.axd" verb="GET,HEAD,POST" type="System.Web.UI.DataVisualization.Charting.ChartHttpHandler, System.Web.DataVisualization, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" validate="false"/>
    </httpHandlers>
  </system.web>
  <system.webServer>
    <handlers>
      <add name="ChartImageHandler" preCondition="integratedMode" verb="GET,HEAD,POST" path="ChartImg.axd" type="System.Web.UI.DataVisualization.Charting.ChartHttpHandler, System.Web.DataVisualization, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
    </handlers>
  </system.webServer>
</configuration>

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