Nikon D6 Reference Manual page 1051

D
Restoring Default Settings
•
Depending on current settings, some menu items and other features
may be unavailable. To access menu items that are grayed out or
features that are otherwise unavailable, try restoring default settings
using the [Reset all settings] item in the setup menu.
•
Note, however, that wireless network profiles, copyright information,
and other user-generated entries will also be reset. Once reset, settings
cannot be restored.
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