To write the entire contents of the scrollback buffer to a file

Ctrl + A and : to get to command mode then:

hardcopy -h <filename>

Cannot open your terminal '/dev/pts/0' - please check

 backup@myserver:~/nginx/20161025$ screen -r 13542
Cannot open your terminal '/dev/pts/0' - please check.

To solve this issue:

backup@myserver:~/nginx/20161025$ script /dev/null
Script started, file is /dev/null

And then I'm able to re-attach to this screen again.