Spent some time working on the problem detailed in Greg's post. Martin eventually provided the instructions on deleting the database (including the user dbx file). So I backed up the existing db by logging in as Guest (that backup included the data collection but not the system collection which contained the users information), then Greg killed the process (as shutdown failed), moved the dbx and log files and restarted the db. Then we uploaded the backup of the db, created the new users and everything seems fine