Direttamente dal sito Microsoft....
Per problemi di accesso al terminal server e per la pulizia della cache delle licenze...
To clean the client's license cache, just delete this key and its subkeys. The next time the client connects to the server, it will obtain another license.
For 16-bit RDP clients, run regedit /v. Then delete the keys under "\Software\Microsoft\MSLicensing" to clean the client's license cache. You can also delete the BIN files from \Windows\System\Regdata.
The RDP client for Macintosh stores the license in a file on the local computer in the folder hierarchy under /users/Shared/Microsoft/RDC Crucial Server Information/. To clean the Macintosh client's license cache, delete the contents of this folder. The client will try to obtain a new license from the server the next time that it connects.
If you delete the HKEY_LOCAL_MACHINE\Software\Microsoft\MSLicensing subkey on a client that is running Windows Vista or a later version, later attempts to connect to a Terminal Server may fail. Also, you receive the following error message:
An Error occurred in the Licensing Protocol
To resolve this problem, right-click the Remote Desktop Connection shortcut, and then click Run as Administrator. By default, the remote desktop connection runs as a user with the lowest user permissions. By default, a restricted user does not have permission to write registry entries to HKEY_LOCAL_MACHINE. Therefore, attempts to rewrite the MSLicensing key fail. Starting Remote Desktop Connection with administrative credentials provides the permissions that are necessary to write the needed registry keys.