check your web.config file
under system.webserver>handlers add or check if exists
<remove name="ChartImageHandler" />
<add name="ChartImageHandler" precondition="integratedMode" verb="GET,HEAD,POST">
path="ChartImg.axd" type="System.Web.UI.DataVisualization.Charting.ChartHttpHandler, System.Web.DataVisualization, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
</add>
also under appSettings
<add key="ChartImageHandler" value="storage=Memory;timeout=30;" />
and under pages>Controls
<add tagPrefix="asp" namespace="System.Web.UI.DataVisualization.Charting"
assembly="System.Web.DataVisualization, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
finally in system.web>httpHandlers
<add path="ChartImg.axd" verb="GET,HEAD,POST" type="System.Web.UI.DataVisualization.Charting.ChartHttpHandler, System.Web.DataVisualization, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35">
validate="false" /></add>
this should fix it for you