Write_form_lines not printing the internal table

Hi,

I'm using write_form_lines to print an internal table in a normal window.This is the code I'm using. The t_header table does not contain any records and there are 10 lines in the itab.But its not printing anything.

CALL FUNCTION 'WRITE_FORM_LINES'

EXPORTING

function = 'APPEND'

header = t_header

window = 'FIRST'

TABLES

lines = itab.

Thanks

Nidhi Jain