'Missing parameter with PERFORM' error with a function IN BACKGROUND TASK

Question

I am getting this error when calling a custom function in MIGO user exit ZXMBCU01.  When I remove the 'IN BACKGROUND TASK' the function works fine and there are no error messages.  When using 'IN BACK...' you can't debug within it to see where the message comes from.  I see the message with SM58.  I am working in an sap 4.7 environment.  I have not found any solutions from google searches.
Here is the statement within ZXMBCU01:
    CALL FUNCTION 'Z_UPDATE_MATERIAL_AVAIL_STATUS' IN BACKGROUND TASK
      EXPORTING
        work_order = xmseg-aufnr.
Here is the code for the function:
FUNCTION Z_UPDATE_MATERIAL_AVAIL_STATUS.
""Update function module:
""Local interface:
*"  IMPORTING
*"     VALUE(WORK_ORDER) LIKE  AUFK-AUFNR DEFAULT '0000000000'
TABLES: eban, resb, aufk.
-Global Types----
TYPES: BEGIN OF t_data,
       rsnum TYPE resb-rsnum,
       rspos TYPE resb-rspos,
       aufnr TYPE resb-aufnr,          "Order Number
       bdmng TYPE resb-bdmng,          "Requirement Quantity
       enmng TYPE resb-enmng,          "Quantity withdrawn
       bsmng TYPE eban-bsmng,          "Quantity ordered against this purchase requisition
       END OF t_data.
DATA:  gt_data TYPE t_data OCCURS 0,
       ga_data TYPE t_data.
-Global Variables----
DATA: gv_refused TYPE BAPIFLAG-BAPIFLAG,
      gs_caufvd  TYPE caufvd,
      g_text TYPE t100-text,
      gv_objnr LIKE aufk-objnr,
      gv_status LIKE  bsvx-sttxt,
      gv_trig_stat TYPE c.
TABLES RETURNED FROM BAPI
DATA:  BEGIN OF xreturn OCCURS 0.
        INCLUDE STRUCTURE bapiret2.
DATA:  END OF xreturn.
  SELECT SINGLE objnr FROM aufk
     INTO gv_objnr
     WHERE  aufnr = work_order.
  CALL FUNCTION 'STATUS_TEXT_EDIT'
    EXPORTING
      flg_user_stat = 'X'
      objnr         = gv_objnr
      only_active   = 'X'
      spras         = sy-langu
    IMPORTING
      line          = gv_status.
  IF ( gv_status CS 'REL' ) AND
     ( gv_status NS 'NMAT' AND gv_status NS 'CNF' AND gv_status NS 'CLSD' AND
       gv_status NS 'TECO' AND gv_status NS 'DLFL' ).
    SELECT SINGLE *
      FROM AUFK
     WHERE aufnr = work_order AND
           ( auart = 'PM01' OR
             auart = 'PM02' OR
             auart = 'PM03' OR
             auart = 'PM99' ).
    IF sy-subrc = 0.
      SELECT resbrsnum resbrspos resbaufnr resbbdmng resbenmng ebanbsmng
        INTO CORRESPONDING FIELDS OF ga_data
        FROM resb LEFT JOIN eban
          ON resbrsnum = ebanarsnr AND
             resbrspos = ebanarsps
       WHERE resb~aufnr = work_order AND
             resb~bdmng > 0.
    SELECT rsnum rspos aufnr bdmng enmng
      INTO CORRESPONDING FIELDS OF ga_data
      FROM resb
     WHERE aufnr = work_order
       AND bdmng > 0.
          SELECT SINGLE bsmng
            INTO ga_data-bsmng
            FROM eban
           WHERE arsnr = ga_data-rsnum
             AND arsps = ga_data-rspos.
          IF sy-subrc <> 0.
            CLEAR ga_data-bsmng.
          ENDIF.
           IF ga_data-bdmng = ga_data-enmng OR
              ga_data-bdmng = ga_data-bsmng.
             "update status - but all items must pass
           ELSE.
             gv_trig_stat = 'N'.
             EXIT. "status won't change so get out now
           ENDIF.
     ENDSELECT.
   IF ga_data~bdmng > 0.
       IF ga_data-bdmng = ga_data-enmng OR
          ga_data-bdmng = ga_data-bsmng.
     IF gv_trig_stat <> 'N'.
          CALL FUNCTION 'CO_IH_USERSTATUS_SET'
            EXPORTING
              I_AUFNR              = ga_data-aufnr    "'000005000263'
              I_USR_STAT_INT       = 'E0002'
  I_USR_STAT_EXT       =
  I_SET_INACTIVE       =
  I_BUF_READ           =
              I_SPRAS              = sy-langu
            IMPORTING
              E_CHNG_REFUSED       = gv_refused
              E_CAUFVD             = gs_caufvd
            TABLES
              RETURN               = xreturn.
          LOOP AT xreturn
           WHERE type = 'E'.
          ENDLOOP.
          IF sy-subrc <> 0.
            CALL FUNCTION 'BAPI_TRANSACTION_COMMIT'.
            RETURN.
          ELSE.
            READ TABLE xreturn INDEX 1.
            CALL FUNCTION 'PI_BP_GET_MESSAGE_TEXT'
              EXPORTING
                iv_message_id     = xreturn-id
                iv_message_type   = xreturn-type
                iv_message_number = xreturn-number
                iv_message_v1     = xreturn-message_v1
                iv_message_v2     = xreturn-message_v2
                iv_message_v3     = xreturn-message_v3
                iv_message_v4     = xreturn-message_v4
              IMPORTING
                ev_message_text   = g_text.
          ENDIF.
     ENDIF.
     ENDIF.
       ENDIF.
     ENDSELECT.
    ENDIF.
  ENDIF.
ENDFUNCTION.
Does anyone have any ideas?  Thank you very much in advance.
Glenn Allen
Software Architect (specializing in SAP)

Answer 1

I'd be starting a process of elimination... perhaps start with an "exit." right after
SELECT SINGLE objnr
  FROM aufk
  INTO gv_objnr
  WHERE aufnr = work_order.
exit.  "leave FM NOW
and if that doesn't crash, work down the code down the code in the function e.g. comment out the BAPI_commit call... and / or build a little test harness report to call the Z function in background task... btw, does the ST22 dump point to anything more specific...?