Session expired problem

That is the usually message for a CSRF verification failure. Per your settings, the CSRF cookie expires after 7200 seconds (2 hours). You may well be logged out, but CSRF is checked before any other processing happens and once the fail is caught execution of the script ends.

Thanks, Dave, your answer lead me to this article:
http://www.johnkieken.com/how-to-handle-...left-open/
I will check it out, it seems that it is possible to redirect to the login page which is good enough for me.