The Chart http handler is not registered. Please, manually add the following line to your Web.config httpHandlers section:
<add path="ChartImage.axd" verb="*" type="Telerik.Web.UI.ChartHttpHandler, Telerik.Web.UI, Version=2008.2.826.20, Culture=neutral, PublicKeyToken=121fae78165ba3d4" validate="false" />