Nona, please excuse my butting in... "On" is a preposition. Whenever you state a date, you need that preposition before the date, "on 9th November". You can of course say "the due date for the payment was 9th November", "9th November" is a predicate, so you don't need the "on"
Omission of 'on' is quite common here in N. America, in business English.
To those who are arguing that the 'on' is required, I would suggest that in formal grammar the date should be written as the ninth of November, 2005. Once you compress the date, it seems to me, it's hard to argue forcibly against further compressing the expression by omitting 'on'.