In ArcGIS for Server 10.1, when accessing a service with ArcGIS Web Adaptor installed, the following error message is displayed:
"HTTP Error 500.24 - Internal Server Error. An ASP.NET setting has been detected that does not apply integrated managed pipeline mode. Detailed Error InformationModule ConfigurationValidationModule."
This error occurs if the .NET Framework settings have been changed for an application pool in Internet Information Services (IIS) Manager. If the .NET Framework was recently upgraded on the system, the .NET Framework settings for all application pools in IIS Manager are changed by default to point to the latest version of .NET.
However, in ArcGIS for Server 10.1, the application pool for ArcGIS Web Adaptor, ArcGISWebAdaptorAppPool, requires .NET Framework 2.0. Hence, the .NET Framework settings for ArcGISWebAdaptorAppPool must be changed back to version 2.0 to resolve this issue.