cannot delete

there are 2 query which will return 0 record when I just select it from table.
but 2 queries are almost same structure but 1 return error and another 1 no error.
anybody know why?

DELETE FROM
(SELECT

FWDBOOK_HBL.COMPANYCODE,FWDBOOK_HBL.BRANCHCODE,FWDBOOK_HBL.JOBNO FROM FWDBOOK_HBL_at_ORACLE8,FWDBOOK_HD_at_ORACLE8 WHERE FWDBOOK_HD.COMPANYCODE = FWDBOOK_HBL.COMPANYCODE AND FWDBOOK_HD.BRANCHCODE=FWDBOOK_HBL.BRANCHCODE AND FWDBOOK_HD.JOBNO=FWDBOOK_HBL.JOBNO
AND (FWDBOOK_HD.CANCEL='Y' OR FWDBOOK_HD.CLSDBO='Y') AND FWDBOOK_HD.BOOKINGDATE BETWEEN TO_DATE('12-12-2001','DD-MM-YYYY') AND TO_DATE('12-12-2006','DD-MM-YYYY')); ERROR at line 2:
ORA-01752: cannot delete from view without exactly one key-preserved table

DELETE FROM
(SELECT FWDINVOICE_DET.COMPANYCODE,FWDINVOICE_DET.BRANCHCODE,
FWDINVOICE_DET.JOBNO,FWDINVOICE_DET.INVOICENO FROM FWDINVOICE_DET_at_ORACLE8,FWDINVOICE_HD_at_ORACLE8 WHERE FWDINVOICE_HD.COMPANYCODE = FWDINVOICE_DET.COMPANYCODE AND FWDINVOICE_HD.BRANCHCODE=FWDINVOICE_DET.BRANCHCODE AND FWDINVOICE_HD.INVOICENO=FWDINVOICE_DET.INVOICENO AND ( FWDINVOICE_HD.CANCEL= 'Y' OR FWDINVOICE_HD.APPROVED='Y') AND FWDINVOICE_HD.INVOICEDATE BETWEEN
TO_DATE('12-12-2001','DD-MM-YYYY')
AND TO_DATE('12-12-2006','DD-MM-YYYY')); 0 rows deleted. Received on Mon Dec 11 2006 - 21:07:33 CST