I had similar problem with Intrepid.
I changed the Gnome login session to "failsafe Gnome" and logged into to
each different user account without any hitches. After that I could use
the normal Gnome session and log in / out & Switch to my hearts content.
Hope that helps.
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Switch User Fails m
Doesn't work for the Guest session, as I don't know how to login in to
this account under failsafe Gnome.
You can get out of the blank screen desktop by pressing "Ctrl + Alt +
Backspace" which brings you back to the Login screen.
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Switch User Fails most of the time
https://bugs.launchpad.net/b
