This error typically occurs when a VyprVPN Premium user already has a registered server, since you are only allotted a single registered server with those account levels. Most commonly this happens if the user deletes their server and fails to deregister the VyprVPN Server first.
To remedy this error, follow the steps in "How do I deregister a server?"
If that does not resolve the issue, or you haven't previously registered a VyprVPN Server, reboot the server from the System Settings section in the web administration panel and try again after it comes back online.
If you need any further assistance, please contact support and we'll be happy to help!