>I would check all of the electrical contacts on the MB-20.
I read that Nikon recommends "isopropyl alcohol" for electrical contacts, which I don't have. Then I thought, "Hmm, alcohol..." In Paris a few years ago, I was presented with a bottle of moonshine "grappa" (distilled left-overs from wine-making). It smells like helicopter fuel and is near damned undrinkable, but I dipped a cotton swab with it and wiped over the MB-20 contacts. And now it works like a charm again - thanks for the tip!