I lost logout session question. How can I get it now?

[Xan]

Hi,

Recently and I don't know why, when I logout from xfce4 (4.0.5), the question 
of what I want to do (save session, logout, ...) does not appear. I don't 
know why. Presumely, I did not did anything new.

So can you help me?. Do you know what could be the most probably thing cause 
it?

Thanks in advance,
Xan.