When I am using emacs under GNU Screen, if I call C-x C-s screen hangs and does not respond to any keyboard input.
I can't reproduce this, but at least one time per day I have to kill my screen session and restart it.
How can I solve this?
CtrlS is the "Pause transmission" (XOFF) flow control character. Usually it's handled by the tty driver, or in this case Screen. Its opposite is XON, or CtrlQ.
When you launch Emacs, it normally takes over most of the special characters (not just flow control, but also the usual CtrlC "Interrupt", for example).
On my system (Linux), Screen does notice when flow control is disabled for the tty. Your OS might have some limitations, though.
I had the same problems with the locked screen and many more when using emacs under screen. For example, C-a in emacs, that brings you to the beginning of the line, gets intercepted by screen and it doesn't work.
Create a file .screenrc in you home directory with the following:
Then each time you open a new screen instead of using C-a you need to use C-u to enter a new screen command. The other two changes take care of a couple more things I needed to change in order to be able to use emacs under screen without problems.