Ich habe den Grund für den Fehler gefunden. Das Problem scheint MS schon bekannt zu sein zumindest steht es im KB-Artikel unter:
support.microsoft.com/kb/2916846 (unter Status)
Folgende Lösung hat mein Problem beseitigt (Quelle: http://guru365.net/2013/04/18/server-2012-terminal-server-license-server-connection-issue/)
There is a known issue for a server 2012 with an instance of RDS license server installed, but not allowing connection to a client.
The error message when trying to connect comes up with something like the following -
A look through the event viewer gave an event relating to the license server expiring its grace period even though it was fully licensed.
This is an issue Microsoft are aware of but as of yet have not realeased a hot fix.
If you come across this take a look at the following key in the registry (of the terminal server license machine)
HKLM\System\CurrentControlSet\Control\Terminal Server\RCM
a key called ‘Grace Period’ is present, this means the license service has not correctly removed this entry
which will force the server to always run in unlicensed mode.
Simply delete the Grace Period key (obviously make a backup beforehand)
You may need to give permission to the admin account you are logged in as in order to delete the key.
The license server will then need rebooting but should allow the connections through after this.
Vielen Dank für eure Hilfe!!!!!!