In Ubuntu 10.4 the "Switch From xxxx..." option does not work, I have to log out and then log in as the other user. It prompts me for my password and eventually puts up an error message as follows .... "Unable to start new display The name org.gnome.DisplayManager was not provided by any .service files" Bilal has responded to me (in Launchpad) that it looks like a Dbus bug and I should report it - which I am. Thanks.
It doesn't look like a D-Bus bug. It looks like an Ubuntu bug or a gdm bug.
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