After the "Load Sample Data" has been done, a User List will be created.
Then, links to the users profile and users list are placed in the User Menu (as per docs).
Login front-end of website and everything works cool.
Next, create a second user list and place link for it in menu.
Now, goto the list manager and edit or delete the original user list that was created from "Sample Data".
Next, goto the front of your website and login. Try to view your profile, or user list.
Try to view the registration page.
They all come up blank!
To correct this, I had to uninstall CB, drop CB tables from database and then do a fresh install of CB.
Now, everything works perfectly!
This time I didn't edit the User List created by "Sample Data", and I am not using a link to it either. (This is still the default User List - just has no menu link to it)
I have instead created a second User List with a menu link.
Everything works fine like this.