Cognos Controller 8.5.1
Windows 2008 R2 Server
Change to Cognos 8 authentication in Cognos 8 Controller configuration, from Native authentication does not change it for the users.
Controller users still get login dialog to enter username and password
On the Windows 2008 server you must start Controller Configuration program by right click and select RUN AS ADMINISTRATOR to allow the changes to be saved.
You do not get a error, but the switch to Cognos 8 is not registered by Windows. Most changes are in newer Windows version not stored correct if you not run the Configuration program as a administrator.
Start Controller Configuration program with Run as Administrator, and change selected authentications method to Cognos 8
Let the user try again.