"Check Keys " looks for duplicate keys. It sorts all the cards by key, then checks
to see if any card has the same key as the preceeding card. It puts up a message telling the number of duplicate keys it found. Get rid of them by using the Dup Key... button.
"Dup Keys..." shows you a pop-up menu with the duplicate keys. Selecting an item will take you to the first occurence of that key. The duplicates will follow it. Look at them by hitting cloverleaf-3 to go to the next card and cloverleaf-2 to go back a card.
Don't use the arrow buttons at the bottom of the cards because those only move to cards of the same type.
Use this to make a new bibliography card; don't use the standard menu command. This sets up some fields when it creates the card.