Christian Einfeldt writes:
Right now, however, we are experiencing a failure of logging into the guest session. Normally, you just choose the guest session in the Lubuntu login screen, and hit enter, and it boots up a full guest session. No password is required.
If the root account can log in (so you know the desktop is installed properly), and it starts to log in but bails out, I'd wonder if there's something in the guest account's .bashrc or .profile, or other login-time configuration files, that are either preventing login or causing an immediate logout.
Have you tried logging in on a console? On the machine, try typing ctrl-alt-F2 to get a text console, and try logging in as guest there. (Ctrl-alt-F1 or Ctrl-alt-F7 will probably get you back to X, but if not, try ctrl-alt- with all the function keys and one of them will probably work.) Or if sshd is set up, try sshing to guest@themachine from another machine and see if you can log in that way; if it isn't set up, log in as root and install openssh-server.
If guest can log in via ssh or text console, but not via X, then you know the problem has something to do with guest's desktop configuration. Try renaming files or directories or copying them from root to see what makes a difference.
If guest still can't log in even on a text console, that makes it a lot easier to debug. With any luck, it'll give you an error message before it logs you out. If the error message disappears too fast, then run script on another machine to record the session, then ssh to the machine. If there's no error message, then from your root login, try putting debug echo lines in guest's .bashrc and .profile, like echo starting .bashrc echo ending .bashrc and so forth; you can use those to see what files are being executed and how far it gets before things go bad.
Good luck!
...Akkana