Hi Kumar,
Please give Field names in capital letters when filling Field Catalog.
FORM build_fcat .
*Build field catalog
wa_fieldcat-col_pos = 1.
wa_fieldcat-fieldname = 'vbeln'. --- this should be Capital letters
wa_fieldcat-tabname = 'IT_FINAL'.
wa_fieldcat-seltext_m = 'Sales document no'. " Column description
APPEND wa_fieldcat TO t_fieldcat.
CLEAR wa_fieldcat.
thanks
sri