Comment 5 for bug 90261

Do you, by any chance, have a file set to load xscreensaver in Settings>Autostarted Applications? I had one that looked like this:

#!/bin/sh

sleep 1 && conky &
xscreensaver &
xmodmap ~/.Xmodmap &
xbindkeys &
adesklets --xfce4 &
mpc update | mpc ls | mpc add | mpc shuffle

I removed the line "xscreensaver &", and it worked perfectly. Hope this helps!