Custom Table Update

How to ensure that the Custom table has happended correctly. With the below code sometimes we have sales orders not being updated in the custom table. Appreciate if anyone has done some checking or log if the update fails.

Example : Sample Code for Locking the table having sales order 123.

CALL FUNCTION 'ENQUEUE_EZ_VBELN3'
        EXPORTING
          mode_ztps_data_buffer = 'E'
          mandt                 = sy-mandt
          vbeln                 = <lfs_input>-vbeln     "sales order 123
        EXCEPTIONS
          foreign_lock          = 1
          system_failure        = 2
          OTHERS                = 3.

      IF sy-subrc  eq  0.
         MODIFY ztps_data_buffer FROM TABLE lt_backlog.      
     endif.


CALL FUNCTION 'DEQUEUE_EZ_VBELN3'
        EXPORTING
          mode_ztps_data_buffer = 'E'
          mandt                 = sy-mandt
          vbeln                 = <lfs_input>-vbeln.

<Added Code tags>

Edited by: Suhas Saha on Nov 11, 2011 2:25 PM