validat

I am having a problem validating PO promised date in Oracle forms personalization . I am using EBS 12.1.3

I am trying ensure the PO promise date is not less than the PO creation date, but I keep getting an error 'not a valid month'.

:PO_LINES.PROMISED_DATE is null    OR
(to_date(:PO_LINES.CREATION_DATE, 'MM-DD-YYYY HH24:MI:SS') > to_Date(:PO_LINES.PROMISED_DATE,'MM-DD-YYYY HH24:MI:SS')
AND :SYSTEM.RECORD_STATUS = 'INSERT')
or (to_date(:PO_LINES.PROMISED_DATE, 'MM-DD-YYYY HH24:MI:SS') < trunc(sysdate)  AND :SYSTEM.RECORD_STATUS = 'CHANGED')

but keep getting not a valid month error ORA-01843