I solved the problem, but it certainly wasn't what I had originally thought. I'd been having problems with someone conducting a password guessing attack against the ADMIN account of my website. Since the attacks were coming from numerous "spoofed" ip addresses, I couldn't block them directly. I decided to create another Administrative level account with a different User Name, assign all ADMIN posts to the new User Name, and delete the ADMIN account. So Far, So Good.
List Manager assigns an owner to each List. Since you can only see the lists that the current logged in User owns, that creates a real problem. Since the "original owner" no longer exists, there's no way for anyone to see any of the lists in the Admin window.
I used phpmyadmin to look at and modify the "wp_lists" database and change the "POST_AUTHOR" (owner of each list). A PROBLEM - The "POST_AUTHOR" field is a tinyinteger (0 to 127) whereas the field "ID" of the "wp_users" database, which is the lookup field of the Owner Info, is a large integer. This means there can be many more real users than truncated List Manager Users. BOTTOM LINE - the "POST_AUTHOR" must be a user with Administrator privileges whose "ID" is 1 to 127!!!
With this editing, everything works fine again.