ITAB_DUPLICATE_KEY

I have written below piece of code

IT_PARTF TYPE HASHED TABLE OF TY_PARTF

         WITH UNIQUE KEY DOC_NUM DOC_ITEM PART_FUNCT,

SELECT

           *

           FROM

               /BIC/AZCPP_O2200

           INTO CORRESPONDING FIELDS OF TABLE

             IT_PARTF

             FOR ALL ENTRIES IN SOURCE_PACKAGE WHERE

               BILL_NUM = SOURCE_PACKAGE-BILL_NUM AND

               BILL_ITEM = SOURCE_PACKAGE-BILL_ITEM AND

               PART_FUNCT = 'ZW'.

and i am getting   ITAB_DUPLICATE_KEY short dump with below message

"\PROGRAM=GP4Y7O1R5M5LSYV5M3H0BLXWT21\DATA=IT_PARTF". However, updating

  the unique table key "PRIMARY_KEY" resulted in a duplicate entry. The key

  concerned may be either the primary key or a secondary key.

  The key components of the duplicate entry have the values "{;000000;ZW}"

  " " " " " ".

Please suggest