Today I came across this error when checking the IIS Authentication configuration with Exchange 2010 and Windows 2008 R2.
The reason this is happening is because the authentication method is being set in both the web.config file and in IIS. To fix it follow these steps:
- on your Exchange server, navigate to: C:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\owa
- make a copy of the web.config file and save it somewhere else.
- modify the original one and remove the entry on line 30 that reads:
- then save the file
This will then elleviate the problem and you will be able to manage your authentication in IIS.