llamar dos veces a 'WRITE_FORM'

[stid]

que tal abaperos, feliz año

hay alguna razón por la cual me deje llamar dos veces a 'WRITE_FORM' pero no me deje una tercera.

me sale "WRITE_FORM não é permitido, porque falta
START_FORM"

CALL FUNCTION 'OPEN_FORM'
EXPORTING
form = 'ZNOVALE_OST_PRU1'
device = 'PRINTER'
dialog = 'X'
language = SY-LANGU
*
*options = ' '
EXCEPTIONS
canceled = 1
device = 2
form = 3
options = 4
unclosed = 5.

IF SY-SUBRC NE 0.
WRITE /'error al abrir formulario'.
STOP.
ENDIF.

loop at T_DATA1.

CALL FUNCTION 'START_FORM'
EXPORTING
startpage = 'FIRST'.

CALL FUNCTION 'WRITE_FORM'
EXPORTING
window = 'CABECERA'.

CALL FUNCTION 'WRITE_FORM'
EXPORTING
window = 'MAIN'.

*CALL FUNCTION 'WRITE_FORM'
*EXPORTING
*window = 'FIRMA'.


CALL FUNCTION 'END_FORM'.
endloop.

CALL FUNCTION 'CLOSE_FORM'.