Problem with function module calling

Question

Hi,
I have two questions here
i have a function moduel 'Z_GET_MATL_BALANCE'
in my code it called in the below said way
CALL FUNCTION 'Z_GET_MATL_BALANCE'
    DESTINATION 'NONE'
    STARTING NEW TASK 'A'
    PERFORMING f_back ON END OF TASK
    EXPORTING
      ref_dte    = s_datum-low
      str_dte    = s_datum-high
      end_dte    = s_datum-high
      i_werks    = p_werks
      i_past     = 'X'
      i_future   = 'X'
      verselem   = p_mrpver
      plscn      = p_scenar
      r_outrec   = r_outrec
      supstk     = p_supstk
      days_ahead = w_days_ahead
      shipnt     = p_shipnt
    TABLES
      mat_bals   = w_zmat_bals_a
      i_zdatum   = i_datum
      mat_movmts = w_mat_movmts_a
      mat_ship   = i_mat_ship_a.
  IF sy-subrc NE 0.
    MESSAGE e005(ZMIM) WITH
   text-009 text-166 text-054 sy-subrc.
  ENDIF.
FORM f_back USING task.
  CASE task.
    WHEN 'A' .
      RECEIVE RESULTS FROM FUNCTION 'Z_GET_MATL_BALANCE'
     TABLES
          mat_bals                     = w_zmat_bals_a
          mat_movmts                   = w_mat_movmts_a
          mat_ship                     = i_mat_ship_a
       EXCEPTIONS
            call_material_lesen_fail     = 1
            call_t450n_fail              = 2
            call_t399d_fail              = 3
            call_aufbauen_mdpsx_fail     = 4
            call_mdezx_aufbauen_fail     = 5
            call_t001w_fail              = 6
            call_zmrpelem_failed         = 7
            call_aufbauen_mdpsx_sim_fail = 8
            OTHERS                       = 9.
      IF SY-SUBRC NE 0.
       RET_CODE1 = SY-SUBRC.
      ENDIF.
now my first question is what is the difference between function modules calling normally and in the above said way
and the second question is
under tables parameter i have four internal tables defined where as while calling the same function module using recive results i have three internal tables. is this correct?
i am asking this because i am getting an error message while using this funciton module
please do not give generic answers, all the helpful answers will get a def reward

Answer 1

Call function starting new task is used to make Asynchronus RFC Call. In this case your function module will be called in a NEW SESSION and it will exceute independently from the Main program which is calling the FM. Also, the main program will continue its own processing and it will not wait for the RFC FM to complete.
Its not mandatory to have all the TABLES parameters in the RETURN Perform (..Receive results from ...)