Sounds like you should contact support!@eventide.com, being sure to say where these units came from, any numbers you have or can see, and when you get this message and from where.
You mean when registering them on eventide.com? You can also get this error message when the units are already registered to a different eventide account. Could you have already registered them? If not, please send an email to support@eventide.com with the serial numbers.
Well, just send the serial number(s) to support@eventide.com. Our support people might contact the previous owner, or they might just deregister them immediately for you. It's up to their discretion.