Event ID 16 — Remote Desktop Services Client Access License (RDS CAL) Availability

Applies To: Windows Server 2008 R2

When a client—either a user or a device—connects to a Remote Destkop Session Host server, the RD Session Host server determines if a Remote Desktop Services client access license (RDS CAL) is needed. The RD Session Host server then requests an RDS CAL from a Remote Desktop license server on behalf of the client attempting to connect to the RD Session Host server. If an appropriate RDS CAL is available from a license server, the RDS CAL is issued to the client, and the client will be able to connect to the RD Session Host server.

RDS CALs are installed onto a license server by using the Remote Desktop Licensing Manager tool.

Event Details

Product: Windows Operating System
ID: 16
Source: Microsoft-Windows-TerminalServices-Licensing
Version: 6.1
Message: The Remote Desktop license server could not return an expired Remote Desktop Services client access license (RDS CAL) to the available pool of RDS CALs because of following error: %1!s!.


No further action is required

The Remote Desktop license server was unable to contact another license server on the network, probably because the other license server was temporarily unavailable. The license server will try again to contact the other license server.

This is a minor warning and there is no impact to the continued functionality of the license server.


To verify that Remote Desktop Services client access licenses (RDS CALs) are installed and available on the Remote Desktop license server, use the Remote Desktop Licensing Manager tool.

To perform this procedure, you must have membership in the local Administrators group, or you must have been delegated the appropriate authority.

To verify that RDS CALs are installed and available:

  1. On the license server, open Remote Desktop Licensing Manager. To open Remote Desktop Licensing Manager, click Start, point to Administrative Tools, point to Remote Desktop Services, and then click Remote Desktop Licensing Manager.
  2. If the User Account Control dialog box appears, confirm that the action it displays is what you want, and then click Yes.
  3. In the left pane, expand All Servers, and then click the license server. In the right pane, the type, version, and number of RDS CALs installed on the license server is listed.

Note:  To verify that the Remote Desktop Session Host server can contact a Remote Desktop license server with the appropriate type of RDS CALs, use Licensing Diagnosis in the Remote Desktop Session Host Configuration tool on the RD Session Host server.

Remote Desktop Services Client Access License (RDS CAL) Availability

Remote Desktop Services