Hi Steve,
Seems like you are using Personal license key. So it only allows you to use it in single site. To use it in another site, you need to remove the key from your old site and re-enter it in new path. Or you can login to http://www.masonrylayout.com/your-account/ and reset you key from there. Please check this video for instructions. https://www.youtube.com/watch?v=KdoOJLMXHtI
Thanks