"An Error occurred in the Licensing Protocol" after resetting a Vista terminal services CAL registry? There is a reason and a workaround!

Long story, short:

When you delete the HKEY_LOCAL_MACHINE\Software\Microsoft\MSLicensing subkey from a Windows Vista system, make sure to launch the Remote Desktop Client afterwards with administrator rights so that the key is recreated properly in the registry.

If you launch the RDP client with a restricted/normal user, the RDP client will not be able to create the proper registry entry.

If you are using the 'new style' Start Menu inside Vista, the easiest way to launch an RDP session with administrator rights is to type into the Start Search field: mstsc

Then, hold down [Ctrl] and [Shift] and then press the [Enter] key. This will launch mstsc (the RDP client) with elevated rights.

Once the key has been created, restricted and normal users will no longer receive the licensing protocol error.

Thanks go out to Paul and Dave at Corporate Computer, my old stomping grounds, for the heads up on this issue and solution. It is also somewhat documented in KB 187614.