License error 0x1B8C: client license already in use

The 30-second fix: Reboot the local machine

Before you touch any settings, just reboot the computer you're connecting from. I know it sounds stupidly simple, but more than once I've seen a stale session hold on to a per-device license after a crash or unclean disconnect. A restart forces the RDS client to release that license. Try the connection again after the reboot.

If the error comes back, the cached license on your machine is corrupt or stuck. Move on to the next fix.

The 5-minute fix: Clear your local RDS license cache

This is the real fix for 98% of cases. The RDS client caches the per-device CAL locally, and if that cache gets out of sync with the server, you get the 0x1B8C error. You need to delete the license key from the registry and let the client request a new one.

Here's what to do:

1. Click Start, type regedit, and hit Enter. Approve the UAC prompt.
2. Navigate to:
   

   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSLicensing

3. Right-click the MSLicensing key and choose Export – save a backup somewhere just in case.
4. Right-click MSLicensing again and choose Delete. Confirm.
5. Close regedit.
6. Reboot the machine.

After the reboot, launch your RDP client again. It will generate a fresh license request to the terminal server. The server will hand out a new license. This works for both per-device and per-user CAL setups.

Why this works: The MSLicensing key holds the cached license blob. When it's gone, the client has no choice but to ask for a new one. If the server has free licenses left, it grants it immediately.

The 15+ minute fix: Force a license renewal on the server side

If clearing the local cache still throws the error, the problem's likely on the terminal server itself. The server might think your client already has an active license that never got returned. This usually happens after a server-side crash, a license server change, or if someone manually deleted the license store.

On the Terminal Server (the machine running Remote Desktop Services), do this:

1. Open Remote Desktop Licensing Manager (search for it in Server Manager or Start).
2. Right-click your license server and select Properties.
3. Go to the Connection method and make sure it's set to Per Device or Per User – whatever your CALs match. If it's wrong, fix it then click Apply.
4. Right-click the license server again and choose Revoke Licenses. This opens a wizard.
5. Select the license(s) that appear to be assigned to the client machine. You can usually spot them by the client name. Revoke them.
6. Wait 2–3 minutes, then on the client machine, clear the MSLicensing key again and reboot.
7. Try connecting.

One gotcha: The revoke process isn't instant. The license server marks the CAL as revoked but it can take up to 5 minutes for the license to become available again. Don't rush it or you'll get the same error.

If you still get the error after that

Check the event logs on the server under Applications and Services Logs > Microsoft > Windows > TerminalServices-Licensing > Admin. Look for event ID 4355 or 4105. These point directly at license allocation failures. If you see a 4105, you're out of available CALs. Time to buy more or recycle old ones.

Also – and this one's a pet peeve of mine – make sure the client machine's name isn't already registered in the AD with a different SID. If you cloned a VM without running Sysprep, the license server sees two machines with the same name but different SIDs. That'll also trigger this error. Re-image the machine properly or remove the stale AD computer object.

That's it. Nine times out of ten, the registry delete does the job. Skip the deeper troubleshooting unless you're sure the server-side licensing is busted.