When I first posted this, I had not rebooted after updating the Host software. I then rebooted it, and still had the problem. However, when I just tried it, it is now working. Not sure how to explain that. Perhaps I got confused, and did not actually try previously - after the reboot. Perhaps something is intermittent.
If it happens again, I will pursue further.
In answer to your other questions:
I was trying to enter the password on the Windows login (lock) screen. It recognized CTRL-ALT-DEL, the Cancel button, and the password enter arrow button. It did not recognize keyboard input, or clicking on the ease-of-access icon.
This server is running Webroot Secure Anywhere. If the problem should recur, I'll try disabling that, and see if it makes a difference.
I am running the Host on a computer with Windows Server 2008 R2. Both Viewer and Host are version 126.96.36.199. When I connect to the Host, I am able to see the screen, and send CTRL-ALT-DEL. I am also able to move the mouse cursor, and it recognizes mouse clicks. However, when I type on the keyboard (to enter the password) nothing happens on the Host side. On earlier version (not sure which), I was able to control this computer without problem.