So I was trying to test the ArcGIS Server Web Adaptor on a Windows 8 virtual machine and it wouldn’t work. I got a 500 error every time I tried to access it.
I completely uninstalled IIS thinking something was wrong with my authentication settings but after re-installing IIS and the web adaptor I still got the same error.
Turns out its to do with the version of .Net Framework used by the web adaptor’s IIS application pool. There is some discussion on this here.
To check the version of .Net used by the app pool open the IIS management snap in and click on the Application Pools option.
This should be set to .Net Framework 2.0. To do this right click the ArcGISWebAdaptorAppPool and select “Basic Settings”. Change the drop down to .Net Framework 2.0, press OK and you should be good to go