sy-subrc info req??

hi

I had seen many time inside loop,if I check the sy-subrc value,but i found it 4 many times inspite of having the records in loop.

IF it_final3[] IS NOT INITIAL.

LOOP AT it_final3.

IF p_doc-low NE 'NB'.

READ TABLE itab_1 WITH KEY banfn = it_final3-banfn.

ENDIF.

IF sy-subrc EQ '0'. -

>here in my loop records are there,but sy-subrc is coming 4.

gt_final2-banfn = it_final3-banfn.

gt_final2-bsart = it_final3-bsart.

gt_final2-badat = it_final3-badat.

gt_final2-werks = it_final3-werks.

gt_final2-udate1 = it_final3-udate1.

gt_final2-ekgrp = it_final3-ekgrp.

gt_final2-ebeln = it_final3-ebeln.

gt_final2-bnfpo = it_final3-bnfpo.

gt_final2-matnr = it_final3-matnr.

gt_final2-menge = it_final3-menge.

gt_final2-bsmng = it_final3-bsmng.

gt_final2-menge1 = it_final3-menge.

APPEND gt_final2.

CLEAR : it_final3.

ENDIF.

endloop.

endif.

here inspite of having records in my intab,this sy-subrc value is 4.

i had seen this prob many time.

plz tell me how it happens & what shd i keep in mind to avoid such cases.

regds.