I had the same problem with Xubuntu 16.04. It happened maybe a week after upgrading from Xubuntu 14.04 (I restart my machine everyday and always do the proposed updates). I could Ctrl-Alt-F1, login and startx to start a normal session. The problem appeared every time I logged in, and I have been using the workaround for maybe ten days before taking time to solve it better: it didn't disappear alone ;-)
Removing the .cache/sessions directory solved the problem. The old directory content is:
I had the same problem with Xubuntu 16.04. It happened maybe a week after upgrading from Xubuntu 14.04 (I restart my machine everyday and always do the proposed updates). I could Ctrl-Alt-F1, login and startx to start a normal session. The problem appeared every time I logged in, and I have been using the workaround for maybe ten days before taking time to solve it better: it didn't disappear alone ;-)
Removing the .cache/sessions directory solved the problem. The old directory content is:
$ ls .cache.old/sessions kobolde: 0.bak -7c7a-4316- aa41-1a78e9658f 69.state kobolde: 1 -120c-4261- 9b1e-79331c3c42 e6.state kobolde: 0 xfce4-session- kobolde: 1.bak
thumbs-kobolde:0 xfce4-session-
xfwm4-203df6e15
thumbs-kobolde:1 xfce4-session-
xfwm4-29d50ede6
xfce4-session-
Hope this can help you to solve the problem.