Hi Mary,
Thanks for all the details! I should be able to help you fix the issue with the registration page.
When you go to Network Settings page in the Network Admin Dashboard (which should be here: http://unewhavendh.org/wp-admin/network/settings.php ), under Registration Settings > Allow new registrations, is “User accounts may be registered” selected? If not, please select this and save changes. Then, check to see if the registration page is now enabled.
If you’re still getting the “page not found” error, can you check the pages on the main site Dashboard (http://unewhavendh.org/wp-admin/edit.php?post_type=page), and let me know if you see a page called Register?
If do see the registration page, you’ll probably want to create a list of whitelisted email domains, so that you can restrict signups to colleagues from your institution. You can find instructions for this here: https://commonsinabox.org/member-registration
I hope this helps, and please let me know if you have any more questions!
Best,
Bree