Reconnecting to a screen session

When there is only one screen session, screen -raAD attaches to the running screen. So far so good.  

However, if for some reason, there are more than one screen sessions, (screen -ls should give you those), screen suggests that you need to do screen -r  [[pid.]tty[.host]] to reattach. 

However, this simply doesn't work at first and yields weird errors like:

There is a screen on: 5541.pts-1.shannon (11/02/2009 04:40:02 PM) (Attached) There is no screen to be resumed matching 5541.pts-1.shannon.

This is utterly confusing, since it first says that there is a screen, but there is no screen to be resumed. What this means actually is just that however: one first has to detach that screen in order to attach to it. So, yes, there is a screen and that screen is not a screen one can connect directly.

The solution is to give the -d parameter to detach it at first, so

screen -d -r  5541.pts-1.shannon

should work. In fact, I guess screen -r -d 554 works too. That 554 portion has to be unique though, so screen -r -d 5 works too if no other screen session starts with a 5.