I've been using 'screen' (yay!). Mostly fine, getting used to it. But then this happened:

# screen -r

There are screens on:

20900.pts-13.server (Dead ???)

29291.pts-1.server (Dead ???)

Remove dead screens with 'screen -wipe'.

There is no screen to be resumed.

What sort of things cause this? I'm guessing it means both screen sessions are completely toast, and the list above is just due to some leftover lock files or something.