How many activations does the Mathworks License Center show? Go to https://www.mathworks.com/licensecenter. Then click on the license of interest and then click on the "Activation and Installation" tab. This will show what machines are currently activated. It's possible the license has already been activated on too many machines and you need to deactivate one. Click on the machine you wish to deactivate and then click the "Deactivate" button. From there you will get a dialog box that does include an option to deactivate a machine that is no longer available.
Good luck,
Eric
