UPDATE - I closed the application. When I reopened it, it displayed the sign in window, and when I pressed "Enter" it switched to a Password window to allow me to complete the sign in.
I clicked on Quicken on the taskbar to open it. I got the update window which ran successfully, and then displayed a sign-in window on top of the Quicken layout. The sign-in window had my username, but nothing else - no password line. How do I sign in?