I'm having this problem on a machine that doesn't have dbus-user-session installed, nor it ever had it installed.
The problem started to appear after installing Google Chrome (although it was quite fresh: I hadn't use it for anything else, apart from opening Firefox to download Chrome).
Note: it was a Ubuntu Server machine "converted" to Desktop by installing the ubuntu-desktop metapackage.
I'm having this problem on a machine that doesn't have dbus-user-session installed, nor it ever had it installed.
The problem started to appear after installing Google Chrome (although it was quite fresh: I hadn't use it for anything else, apart from opening Firefox to download Chrome).
Note: it was a Ubuntu Server machine "converted" to Desktop by installing the ubuntu-desktop metapackage.