single-row subquery returns more than one row

CURSOR CUR IS

SELECT T.bom_header,

T.sap_cage_cd,

I.part_doc_nbr,

I.cage_cd,

P.ec_revision_mfg,

(SELECT NVL (I2.sap_xref_no, I2.part_doc_nbr)

FROM eissap.tbitem i

WHERE I.item IN (SELECT comp_part

FROM eissap.tbpart_config_comp_config

WHERE item = comp_part)) AS sap_xref_no

,

C.comp_config,

C.qty_per_mfg,

C.unit_of_measure_cd,

I.item

FROM TEMP_SAP_BOMS_LIST_BKP T,

EISSAP.TBITEM I,

EISSAP.TBPART_CONFIG_COMP_CONFIG C,

EISSAP.TBPART P,

EISSAP.TBITEM I2

WHERE (T.bom_header = I.part_doc_nbr OR T.bom_header = I.sap_xref_no)

AND T.sap_cage_cd = I.cage_cd

AND I.item = C.PART_ITEM

AND I2.ITEM = C.COMP_PART

AND I.item = P.item

AND c.config = (SELECT MAX (c1.config)

FROM EISSAP.tbpart_config_comp_config c1

WHERE c1.part_item = C.part_item);

FOR C4 IN CUR LOOP

INSERT INTO TEMP_SAP_BOMS

bom_header,

sap_cage_cd,

part_doc_nbr,

cage_cd,

ec_revision_mfg,

sap_xref_no,

comp_config,

qty_per_mfg,

unit_of_measure_cd,

VALUES(C4.bom_header,

C4.sap_cage_cd,

C4.part_doc_nbr,

C4.cage_cd,

C4.ec_revision_mfg,

C4.sap_xref_no,

C4.comp_config,

C4.qty_per_mfg,

C4.unit_of_measure_cd,

C4.item);

CLOSE CUR;

END LOOP;

END;