If an unlicensed client connects to a Terminal Server for the first time,
the Terminal Server issues the client a temporary Terminal Server Client Access License (CAL) token.
After the user has logged into the session, the Terminal Server instructs the License Server to mark the issued temporary Terminal Server CAL
token as being validated. The next time the client connects, an attempt is made to upgrade the validated temporary Terminal Server CAL token
to a full Terminal Server CAL token. If no license tokens are available, the temporary Terminal Server CAL token will continue to function for
90 days. The license is stored in the client's registry.
Thirty-two bit RDP clients store their license under the key
HKEY_LOCAL_MACHINE\Software\Microsoft\MSLicensing.
You can also delete these key from batch file, To download batch file for windows XP Click Here
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.
