login screen hangs when I try to switch users without disconnecting VNC client I'm fast-user switched to the login screen.  However, when I start to type my user name and password the keyboard input freezes before I am finished and I get the spinning beach ball and can't log in.  Sometimes if I hit any of the volume buttons the keyboard unhangs and I am able to log in, but this time this isn't working any more.

This only seems to happen if I forget to properly disconnect a VNC client before switching to the login screen.  I still have ssh but I am not sure what process to kill to resolve the problem.  There aren't any processes running the look like a VNC server.  I have looked for any process containing the substring "ARD", "VNC", "Lock", and "Remote" (case insensitive, e.g. ps aux | grep -i ...).
I have run into this problem many times before. To get it to work, try disconnecting after entering your password, wait a few seconds, and then connect again.