Can’t resume screen, says I am already attached

Here's a script that should work for you.

#!/bin/bash

function chooser {

    echo
    echo "I found the following screen sessions: "
    echo

    pcount=0

    # 
    # find the session dir
    #
    sessdir=$( screen -ls | egrep 'Socket' | awk '{print $NF}' | sed -e 's/\.$//' )

    #
    # enumerate existing sessions, and add them to the plist() array.
    #
    for screen in $( find $sessdir -type p ); do
            pcount=$((pcount+1))
            pname=$( basename $screen )
            pdate=$( ls -latr $screen | awk '{print "( "$6" "$7" "$8" )"}')
            plist[$pcount]=${pname}
            echo "  [$pcount]       $pname   $pdate"
    done

    echo
    echo -n "Please select a session to reconnect to: "
    read choice

    # 
    # if the selected choice doesn't exist, recycle the chooser.
    #
    if [ -z ${plist[$choice]} ]; then
            echo
            echo "Your choice [$choice] is invalid.  Please try again."
            echo
            sleep 1
            chooser
    else
            screen -r -d ${plist[$choice]}
    fi

}

#
# the chooser function does all the work
#
chooser

I didn't distinguish between sessions that are currently attached or detached, so you may have to do that yourself if it matters to you.

As screen -r says, there is one screen, but it is attached. To resume it on your current terminal, you have to detach it from the other one first: screen -d -r 27863, see manpage -d.

Edit: use -d instead of -x.

Edit2: @alex78191: When using -x, screen attaches to the currently running session, resulting in a "multi-display mode": you see the session on both terminals simultaneously, i.e., when entering a command on one terminal, it also appears on the second. However, detaching from a multi-display mode just detaches the current terminal. You hence get the message that it is still attached (on the other terminal).