FAST ESP : Duplicate items when searching

Question :
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I'm getting a lot of identical hits for the same item. What have I
done wrong?

ANSWER:
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There are several possible causes for this, but the most common cause
is that the document ID is not present in the document summary.
Unless you've explicitly disabled incremental indexing, the first
entry in the first document summary class MUST be the document ID. If
not, incremental indexing will not work, and you will get lots of
duplicate items.