Is there any documentation that you are following?
Just standard wordpress updates. It says my site isn't registered, even though it has been for several years. I deleted the old key and created a new one, it still won't accept it.
When re-registering the site, did you use the link from the WP admin installer page, or did you add the site on your account page here on toolset.com?
The URL needs to be exactly correct (including the http protocol), and it is easy to introduce minor differences when adding the site manually on toolset.com and so it is always safer to follow the register link from the installer page (which automatically passes the correct URL).
If having done that you still have problems, can you check the installer debug info (you can navigate to it by going to the bottom of the page at Toolset > Settings and clicking the Toolset debug link, and from the resulting page click the Installer Support link.
That page includes a log section which may contain useful information pointing to the source of the problem.
The problem here is with the URL that you're using the register the site. Your website will actually send this URL to our servers when you click on Get Key for this site when you've clicked the registration button.
The URL you should be using is hidden link
Please register with the above URL and let me know if your registration works.