Shutdown failed

[ceH9l_]

Could anyone please help me with shutdown option?
After finishing playback I can see 30 sec countdown and then this message:
"This is a message from SMPlayer
The computer should shut down now.
However shutdown failed."
And nothing happens.
Any idea why?
SMplayer 16.40
Ubuntu 14.04.2 LTS

[rvm]

Shutdown the computer in linux is not that easy. SMPlayer tries to communicate with the gnome session manager to request the shutdown. If it fails then it tries with the kde session manager, if it fails it tries with the power manager dbus interface. If it fails it displays the message you saw.

[ceH9l_]

Does it mean that this option doesn't work with linux? Or may be I should make any changes to these session/power managers to allow shutdown?
(all of them or at least one will be enough?)

[rvm]

It should work on Gnome and KDE, at least. Although I think I also tested it on lxde and it worked too.

What desktop are you using?

[ceH9l_]

Desktop is XFCE 4.
I had previously installed 32-bit version of Ubuntu with XFCE desktop and used another mediaplayer - XBMC, had the same problems with shutdown, but solved it somehow - but totally forgot how!