Replace the tag <httpHandlers/> with the following:
<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>
Add a tag in web.config entry for <handlers> as follows:
<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" />
Add a tag in web.config entry for <appSettings> as follows:
<add key="ChartImageHandler" value="storage=file;timeout=20;dir=c:\Temp\;" />
Create directory "~/_layouts/ChartImages/" folder in the Templates directory and give authenticated users full permission
Create directory C:\Temp and give full permission to the Application Pool identity for your web application
Once you have completed the steps you will need to activate the site collection feature “DocuChart”. After activating the feature you should see the web part “DocuChart” show up in the web part gallery.