Solution:
Add the following handlers to the Web.config if they are missing:
<system.webServer>
<validation validateIntegratedModeConfiguration="false" />
<handlers>
<add verb="*" path="*.aspx"
type="ThoughtWorks.CruiseControl.WebDashboard.MVC.ASPNET.HttpHandler,ThoughtWorks.CruiseControl.WebDashboard"
name="CCNetHttpHandler" preCondition="integratedMode" />
<add verb="*" path="*.xml"
type="ThoughtWorks.CruiseControl.WebDashboard.MVC.ASPNET.HttpHandler,ThoughtWorks.CruiseControl.WebDashboard"
name="CCNetXmlHandler" preCondition="integratedMode" />
</handlers>
</system.webServer>
If the handlers are present, add preCondition to each one of them:
preCondition="integratedMode"