Actually you are partially correct; yes you should contact support for a matter like this, but this brings up a very common experience we in Support have almost daily, and I believe it will make good to bring to the forum.
-Customers will email Support when they receive an "Invalid serial number' message when attempting to register a previously owned product. 99% of the time it is because the previous owner has not unregistered it from his/her account. Here is what owners and buyers alike should do:
1. If you are selling your Eventide product that is registered to you; please be mindful of the future owner and unregister it so that they can register it without issue.
2. When purchasing a previously owned product, ask the person from whom you are buying from if they have it registered, and if they do, to unregister it so you can do so without issue. Sometimes the owner may have forgotten their account info, so usually Support will be contacted at this point to change accounts when both parties are involved; however what occurs most often is that the previous owner forgets about the registration and Eventide (as a courteosy) contacts the previous owner to confirm they no longer own the product in question.
However for any questions or difficulties that may arise with any product registration, feel free to contact email@example.com