SET PARAMETER AND CALL TRANSACTION

Hi,

in my hierarchical ALV i´ve got the following code when double cliking a row:

form frm_alv_user_command USING UCOMM LIKE SY-UCOMM

SELFIELD TYPE SLIS_SELFIELD.

case ucomm.

when 'VER_PEDIDO'.

CHECK NOT selfield-tabname IS INITIAL.

IF SELFIELD-TABNAME = 'GT_ITAB'.

IF SELFIELD-FIELDNAME = 'VBELN'.

CLEAR gt_itab.

read table gt_itab index SELFIELD-TABINDEX.

if sy-subrc = 0.

FREE MEMORY ID 'AUN'.

SET PARAMETER ID 'AUN' FIELD GT_ITAB-VBELN.

CALL TRANSACTION 'VA23' AND SKIP FIRST SCREEN.

endif.

endif.

endif.

endcase.

The problem is that when i go to transaction VA23 i always get the last value shown in the transaction and not the one i´ve double clicked in the ALV.

Why is this happening?

Best regards.