As Barry pointed out: Validating the license did take 2 tries. Closing and restarting Excel confirmed the change to full version.
After reading his post, I reopened and tried the Registration Key again. The second time it accepted the Key. I closed and reopened Excel and the program is now registered.
Obviously, the Registration needs to be fixed so you don’t get an error the first time you try the key. I installed the program on a second computer and got the same result. The first time I click to register the key I got the error. Clicked on it a second time and it worked!