I diagnosed the problem. I have JRPassphrase (
extensions.joomla.org/extension/jrpassphrase) installed, and I have to deactivate this to get the admin pages to load. The reason there is a conflict is that I had used jfbconnect for the new user registration and it was looking for that term to redirect to the question to avoid the robots signing up. I disabled that and now can get to the admin pages.