Thanks for your bug report. Which version of gdm do you use? Can you run
sudo gdmsetup
from the command line and paste the full output here?
** Changed in: gdm (Ubuntu)
Importance: Undecided => Medium
Assignee: (unassigned) => Ubuntu Desktop Bugs
Status: Unconfirmed => Needs Info
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Cannot run gdmsetup
https://launchpad.net/bugs/66034