When you perform some actions in the Control Center GUI, such as running LiveUpdate, you see the error "The Scanner has been deleted by another user and no longer exists". Virus Definitions on the Dashboard may also be out of date, even though they are up-to-date when you check each scanner individually.
The Scanner has been deleted by another user and no longer exists.
At some point a scanner was not cleanly removed from the Control Center and orphaned entries still exist in the configuration database that point to the scanner.
To resolve this issue you will need to refresh the database by returning to factory defaults to remove the bad entries. Full backups and Configuration backups will still contain the orphaned entries, so you will need to either use a "Policies only" backup to restore or reconfigure the appliance from scratch.
Once the database has been restored without the orphaned entries, the issues will be corrected.