Check that the version of the license server supports issuing RDS CALs to the Remote Desktop Session Host server. The license ...

Check that the version of the license server supports issuing RDS CALs to the Remote Desktop Session Host server. The license server must be running the same (or a more recent) version of the operating system as the RD Session Host server. You might need to upgrade your license server to an appropriate operating system or install a new license server with the appropriate operating system.