Failing to update internal table(deep structure) using a work area.

Hi guys

I am trying to update an internal which is within another table.Its actually a deep structure but when i try to update it its giving me a short dump.

Below is my code

*declaration of variables

DATA: it_levy TYPE LB_T_BIL_IT_KOND,
wa_levy LIKE LINE OF it_levy.

*reading the data from the internal table to my work area
READ TABLE IS_BIL_INVOICE-IT_KOND[] INTO wa_levy
WITH KEY BIL_NUMBER = GS_IT_GEN-BIL_NUMBER
ITM_NUMBER = GS_IT_GEN-ITM_NUMBER
KSCHL = 'ZWNT' BINARY SEARCH.

*Update certain fields and update the final internal table
IF wa_levy-KSCHL = 'ZWNT'.
wa_levy-ITM_NUMBER = '000011'.
wa_levy-KPOSN = '000011'.
MODIFY IS_BIL_INVOICE-IT_KOND[] FROM wa_levy. *I'm getting a short-dump here
ENDIF

error-table.jpgerror-table.jpg

I have also attached a screen short of the short dump

Regards

Bryan