zvbeln should generate automnatic number

hello

i have a problem regarding auto generate of temp sales order number.

when i debug this program it shows some number in zvbeln but when i execute the program it automatically saved the program but the temp no. is not saved in ztable.

the program is as under :-

SET PF-STATUS 'SAVE'.
*CASE SY-UCOMM.


* END
* CASE SY-UCOMM.
* WHEN 'SAVE'.
*break-point.
*WHEN 'SAVE'.
IF SY-UCOMM = 'SAVE'.


.
SELECT MAX( ZVBELN ) FROM ZLIPS INTO P_VBELN WHERE VBELN = WA_ZLIPS-ZVBELN.

WA_ZLIPS-ZVBELN = P_VBELN + 1 .



*BREAK-POINT.

move wa_zlips-vbeln to wa_final-vbeln.
move wa_zlips-posnr to wa_final-posnr.
move wa_zlips-MATNR to wa_final-MATNR.
MOVE WA_zlips-ZIEME TO WA_final-ZIEME.
MOVE WA_zlips-UMZIZ TO WA_final-UMZIZ.
MOVE WA_zlips-MEINS TO WA_final-MEINS.
MOVE WA_zlips-UMZIN TO WA_final-UMZIN.
MOVE WA_zlips-WERKS TO WA_final-WERKS.
MOVE WA_zlips-ERDAT TO WA_final-ERDAT.
MOVE WA_zlips-MAKTX TO WA_final-MAKTX.

append wa_zlips to it_zLIPS.
* APPEND WA_ZLIPS TO IT_FINAL.

modify zlips from table it_final.

if sy-subrc = 0.
MESSAGE : 'NEW TEMPORARY ORDER NO.' TYPE 'I'.
endif.

ENDIF.

MESSAGE : 'DATA HAS BEEN SUCCESSFULLY SAVED' TYPE 'S'.

*WHEN 'BACK'.
IF SY-UCOMM = 'BACK'.
LEAVE PROGRAM.
ENDIF.
* WHEN 'EXIT'.
IF SY-UCOMM = 'EXIT'.
* LEAVE TO SCREEN 0.
LEAVE PROGRAM.
ENDIF.
* WHEN 'CANCEL'.
IF SY-UCOMM = 'CANCEL'.
LEAVE PROGRAM.
* LEAVE PROGRAM.
ENDIF.