Same problem on fresh install of 14.04 and the workaround from https://bugs.launchpad.net/ubuntu/+source/xfce4-power-manager/+bug/1222021 of editing /etc/systemd/logind.conf is effective.
Same problem on fresh install of 14.04 and the workaround from https:/ /bugs.launchpad .net/ubuntu/ +source/ xfce4-power- manager/ +bug/1222021 of editing /etc/systemd/ logind. conf is effective.