An ASP.NET setting has been detected that does not apply in Integrated managed pipeline mode.
This error is because of configuration in the system.web > httpHandlers section. To fix this while maintaining integrated mode, add the following markup to your application's web.config in the configuration section:
<configuration>
<system.webServer>
<validation validateIntegratedModeConfiguration="false"/>
</system.webServer>
</configuration>
Adding <validation validateIntegratedModeConfiguration="false"/> addresses the symptom, but is not appropriate for all circumstances. Having ran around this issue a few times, I hope to help others not only overcome the problem but understand it.