So after spending countless number of phone calls, and emails with tech support only to tell me that the only solution to not being able to register kindle on my desktop Mac that I would have to use the internet version of kindle I tried a few things and then I figured out how to make it work.
In order to make Kindle 1.20.3 to work you have to download an old version of kindle first then install it. what ever you do DO NOT UPDATE THE APP UNTIL AFTER YOU REGISTER. Once you have registered then you can update to 1.20.3 and you'll still be able to use kindle.
Hope this helps someone. Google Kindle 1.17 download and you should find several links to download.