Product:
Cognos Controller 10.2.1
Windows 2012 R2 Server

Symptom:
User cannot login to Cognos Controller – they are prompted for user and password; with the old login dialog box you have when you run NATIVE login to Cognos Controller.
There worked yesterday to login with CAM SSO, that is connected to the Active Directory.

Possible Solution:
Login to the Cognos Controller applications server as administrator.
Right click on Controller Configuration and select “Run as Administrator”.
Go to the Server Authentication tab.
Change the “selected authentication method” from CAM Authentication to NATIVE.
Click on SAVE icon.
Change the “selected authentication method” from NATIVE to CAM Authentication.
Click on SAVE icon.

Then ask the users to try to login with the Cognos Controller client again. If all is well then should come in.

If that does not help, restart the Controller Applications server in a controlled manner.
This issue can have come from a reboot of the Controller Windows server, and some Controller services have not loaded correctly.

Remember to always use “run as administrator” when you change in configuration. Otherwise your changes are stored in folder c:\users\%username%\appdata\local\virtualstore\program files\ibm\cognos\ccr_64\data\.