When the importing the constituents that return this exception into a revenue update batch, they are flagged as duplicates.  This could have been manually corrected, but was not.  Therefore, instead of updating the record when running the batch committal process, the system tried to insert a new record with the same lookup ID.  This failed because of the unique constraint requirement.  The reason each constituent was flagged as a duplicate was that the constituent had the SAME lookup ID with a different type code.