Hello, I am having the same issue, and would love help in getting this resolved. I get as far as the "Welcome, {User}!" view, but any attempt to create an account give the "Unable to save user..." message.
I have tried it with multiple templates, including JA purity, to ensure it isn't a problem with my customizations (I edited loginregister template on my main template -- for testing, I kept the JA Purity template as the default, but there is a template switch module on the left -- change it to jcb_naturallyborn if you like

).
My site is naturallyborn.net.
I will send admin login information via Contact Us form.
Thanks in advance! This is the last piece of the site to put in place before launching, so your help would be MUCH appreciated!
Amy (aphils)