Sandra, There have been reports that the Nikon D3's metering selector switch exhibits the behavior you are describing. I experienced it on my D3. I don't know if the switch is faulty or just finicky. Try moving the switch to "Centerweight" then back to "Spot" and them make sure the switch is fully reseated in the lock position. If this does not resolve the issue, leave the switch in the "Matrix" position and assign the "FUNC" button to activate spot metering. It is option "f4" in the Custom Settings menu.
Hope this helps...JL
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