from http://support.microsoft.com/kb/885013 we read:
If this event is logged on the Terminal Server, you must make the registry changes on the Terminal Server. If this event is logged on the Terminal Services Licensing Server, you must make changes on the licensing server.
This symptom occurs if the following conditions are true:
* The Windows Server 2003-based domain has Windows Server 2003 Terminal Server License servers with Terminal Services Per User Client Access License (CAL) tokens installed.
* The Windows Server 2003-based domain has Windows Server 2003 Terminal Services servers running in Per User mode.
This issue occurs if the LicensingGracePeriodEnded registry entry is not set. The LicensingGracePeriodEnded registry entry suppresses the event messages that appear in the System log and ends the Terminal Services license count-down process
To resolve this issue, add the LicensingGracePeriodEnded registry entry to the registry. To do this, follow these steps:
1. Click Start, click Run, type regedit in the Open box, and then click OK.
2. Locate and then click the following subkey:
3. On the Edit menu, point to New, and then click DWORD Value.
4. Type LicensingGracePeriodEnded, and then press ENTER.
5. Right-click LicensingGracePeriodEnded, and then click Modify.
6. In the Edit DWORD Value box, make sure that the Value data box contains a NULL value (0), and then click OK.
7. Quit Registry Editor.