Flat file to IDOC Problem

Hello All,
We are facing a problem in mapping a flat file data to an IDOC segment.

The steps we are following are :
Upload the flat file and converting the flat file to the record list. ( This is working fine)
Then looping the record list, and mapping the record list fields to the fields of the IDOC Segment structures. This is not functioning as desired.

The record list definiton is

Top (always a single record)
Header (always a single record)
Items (multiple records)
Trailer (always a single record)

The loop is to fetch the different items and the “In Array” definition is “Data/Top/Header/Items”

But the Map statement within the loop is not fetching the values when it is mapped to the IDOC Structure fields. The end result is IDOC Structure is null. The values are fetched when the input and output structure names are the same.

Help in this regard is very much appreciated.
Thanks in advance