In some instances, Terminal Server or Remote Desktop client access licenses are not validated properly by the server. The user may see the following message:
“The remote computer disconnected the session decease of an error in the licensing protocol. Please try connecting to the remote computer again, or contact your server administrator.”
In most cases, removing the HKEY_LOCAL_MACHINE\Software\Microsoft\MSLicensing key and its subkeys solves the problem. However on Vista and Windows 7 clients, the problem may persist.
In that instance, right click the RDP shortcut and select Run as Administrator when starting the session. This allows the registry keys to be correctly re-written. For more info, click here.