Sony DVS-9000 System User Manual page 867

Note
If there are already one or more locked menus, selection of lock candidates is
not possible.
In this case, the indication of the [Lock Item Select] button changes as follows.
When the displayed
menu is locked
If you want to select lock candidates, first remove the lock in the Setup
Operation Lock menu.
When a menu other
than the displayed
menu is locked
System Maintenance (Maintenance Menu)
867