On a Server 2012 RDS farm that has been deployed and working for some time you begin to receive errors stating ‘The remote session was disconnected because there are no Remote Desktop License Servers available to provide a license. Please contact the server administrator.”
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.
Note: You will need to give administrators read and write access to the key or you won’t be able to delete it. Also please observe the usual precautions when working with the registry and take a backup first.
Give your session hosts a reboot and all should be well.
***UPDATE***
So as many will by now have noticed the above fix is actually temporary and must be repeated every 120 days. I looked back into this recently to see if there is yet a hotfix for it and there sort of is although it appears Microsoft don’t have any confidence that it is actually a permanent fix and I can’t yet verify whether it is or not, some people seem to be saying it doesn’t work and some are saying it does.
http://support.microsoft.com/kb/2916846
Give it a try and would be great if people could leave comments to let us all know whether it works for you