You verify your configuration is as expected, that you have valid CALs installed on a Server 2012 terminal server licensing server and that the RD Licensing Diagnoser doesn’t report any errors.
The issue may be that there is a bug with Server 2012 RDS session hosts where they will not look to the licensing server for CALs when the grace period ends. Microsoft are reportedly aware of this but as yet there is no KBA or hotfix for it.
The solution is to open the registry editor on the affected session hosts and browse to the following:
HKLM\System\CurrentControlSet\Control\Terminal Server\RCM
If the ‘GracePeriod’ key exists you will need to delete it.
