I had a similar problem with a Demo bought from BestBuy.
To lock or unlock the navigation discs inside the drive, follow the procedures listed below.
AVIC-D3:
While the unit is turned on, press and hold "MENU" and "Back (Track Left)" buttons simultaneously. Next, push and release reset button. Continue to hold "MENU" and "Back (track left)" until the unit reboots.
Then push eject button, NAV disc should eject.
Follow same procedures to lock Nav disc.
Hope this helps.